There are some conditions for reproduction.

・ Line with arrow
・ Set gradation to line color
Two or more lines created by the appearance

It is good to change the line width or move by "deformation" to check the change of the overlapped line.

Rotate the object.
Then click on the eye icon in the appearance panel to show or hide each line. The direction of the gradation of the line not touching should change one after another.

I have confirmed this phenomenon in all versions from CS6 to 2020.
A similar phenomenon was obtained with the vertical axis reflect. In my tests it didn't happen with horizontal reflect.

What!

<Japanese>
再現のためにいくつかの条件があります．

・矢印のついた線
・線カラーにグラデーションを設定
・アピアランスによって作成された2つ以上の線

重なった線の変化を確認するため，線幅を変えたり"変形"で移動しておくとよいです．

オブジェクトを回転します．
そして，アピアランスパネルの目のアイコンをクリックしてそれぞれの線を表示，非表示してみてください．触っていない方の線のグラデーションの方向が次々に変わるはずです．

私はこの現象をCS6から2020までのバージョン全てで確認しました．
また，垂直軸のリフレクトでも同様の現象を得ました．私のテストでは水平軸のリフレクトでは起こりませんでした．

何ということでしょう！

Hi, I am a design professor and most students in my class experienced a specific problem when we were doing an exercise to learn how to apply the correct color palettes to different logo files. Specifically, we created fictional identity designs as a means to learn how to create a production-ready bundle of files (a logo with versions in b&w, spot color (Pantone), 4-color process, and RGB). Almost 100% of my 18 students had their 4-color process file -- which was filled with CMYK colors upon designing, and should have stayed CMYK -- show up as being filled with RGB when opened after having been closed.

Through testing this unusual pattern of error across all of their files, it appears that Adobe Illustrator will choose to show colors in the color palette that was last opened within the application, and if the palette isn't the same as the fill colors, it creates a color translation of what the color should be into what it want to show you. Stated another way, the students had trouble getting the color palette to hold the color information they entered (percentages/values of either CMYK or RGB, in particular). Regardless of what they had entered, a computer with one or the other of these color palettes open would override their settings. Unacceptable. In one case, I also witnessed a student manually enter RGB values, only to deselect the item, select the object again, and then find different RGB values in place than those I watched him enter. In 19 years of teaching, I've never seen this problem be so widespread across student files.

For what it's worth, the Pantone palette behaved. The problem specifically is between RGB and CYMK colors/color palettes. PLEASE FIX THIS. This will cause major problems in real projects that rely upon color mode accuracy. Please contact me with information about the problem and/or solution. We would appreciate a follow-up.

I have a collection of swatch colors that I save, and for some reason, they are all getting dull. A bright orange to darker gradient turns to a muddy orange and all of the swatches are dull. I copy the logo from an older file and realize how dull my colors have become. You can see how dull the colors have become in the attached image. Also, the Graphic Styles have become duller. You can see the new refreshed colors form a different file with the two swatches at the middle bottom of the Graphic Styles window. This is a VERY serious problem, because all of the colors on my artboard have switched to these duller colors, so I have to update them to the original. Not sure why this is happening, but it needs to be fixed.

Also, is there a way you can make a global gradient change an option that you have to choose to do, because it's changing gradients that I don't want changed. Both of these problems are VERY FRUSTRATING and waste my time.

I know that AI's eydropper pick color not directly form raster image, but from it's preview, but I think it's terribly wrong, when you pick a color from a CMYK image placed inside CMYK document and get mutated color.
For example, I have photo blended into single colored background and I don't remember which one exactly. I pick this color with eyedropper inside AI to match image edge with vector background and it almost looks OK, but when it's printed, the mismatch is quite visible.
Other people, whose designs I dissect quite often, seem to forget or more likely don't know about AI picking colors (because it's not natural), and if I don't find it, I got all the blame.

Using the latest version of Illustrator CC, when I open a particular logo (a multi-layered object with active strokes) and make any changes (ex: outline strokes, rotate, re-scale, etc), I experience a color dulling and color changes to the entire logo.

Oddly enough this only happens with the RGB version of the logo, not the CMYK version of the logo. And when I cmd-z these actions the color dulling / color changes won't revert back. In all of my years using Illustrator I've never witnessed this strange behavior, which is why I assume this is a bug.

Even stranger, after the color changes appear, when I try applying the same exact color swatch to all layers, some of the colors still remain dull. For example, if I select the leaf in the artwork (which consists of a color fill and a stroke) and I apply the same color swatch to both the color fill and stroke, the stroke shows a dull color, yet the color fill shows the actual color. Even though all layers and groups show 100% opacity. The file has been set to RGB color mode, has been converted to RGB, and I'm using RGB swatches.

Can someone please look into this? I'm unable to make edits to my files. Could this be a result of opening a PDF file that was created in a past version of Illustrator on another computer? I wouldn't think that would be the issue since the file doesn't use anything fancy (just brush strokes and color fills), and this doesn't explain why I'm not experiencing these problems with the CMYK version of the same exact artwork.

When I click and drag the eyedropper tool outside of Illustrator to sample a color from something else (a website, pdf document, etc.), the color isn't correctly picked up.
For example, if I move the eyedropper over something orange, it shows in Illustrator as blue or black; even if I sample a large white space, it shows in Illustrator as a different color. It seems to only be showing sampled colors as white, neutral, black/gray, and shades of blue.
The program is up-to-date.
I tried it in two browsers, Chrome and Safari, and the results were the same in both.
I tried quitting and restarting Illustrator and both browsers and nothing changed. When I sample colors inside of Illustrator, it reads correctly.

I am using the newest version of Illustrator. Within the last week or so, my generic CMYK color palette has changed. The percentages that make up the color are different on nearly every color. My black color swatch used to be 100% black. Now it is C:74.97 M:67.92 Y:67.05 K:90.15. Everything in my document is set to CMYK. I changed nothing. My yellow is C:6.18 Y:96.55. It used to be 100% yellow. All of the colors have this issue. Please let me know how I can get this back to the normal way. I've been using Illustrator for the last 23 years and have never experienced anything like this.