Core Graphics has a bug with the extend color for radial gradients, which we'll need to work around. See attached testcase.
Created attachment 77831 [details]
Created attachment 77845 [details]
This bug is also apparent in LayoutTests/svg/batik/paints/gradientLimit.svg
This patch will require new pixel results for various SVG, CSS and canvas tests. Also, some of the canvas/philip tests break (and some get fixed).