In the image below you'll see two gradients:
- Both were made in Illustrator (CC 2019, v23.1)
- Both use the colors #ee2d38 and #624a9e
- Both swatches are set to the same Color Mode as the Color Space
- Color space (RGB vs CMYK) is not a factor as issue occurs in both
The difference is:
- Top one goes from Red to Purple using the Gradient Tool
- Bottom one has two layers: Red to Red Gradient with Opacity 100% to 0%, Purple only layer underneath
This does not happen in Freeform Gradient, only Linear and Radial.
Clearly Illustrator can render the desired result in Freeform and the workaround. This happens with many gradients I try an make. Honestly, it's the largest reason I don't design with gradients at all. I can't find a single guide, answer, tutorial, or article anywhere that explains why this happens and how to correct it. I got the workaround for the bottom from a Color to Black workaround but never an explanation of why so I can avoid and self correct in the future.
Side note: Muddy Gradients would be a great Jazz Band