It should be possible to generate the color gradient somehow. Adobe does this with a canvas. This open source project has accomplished this feat: iro.js
~The problem is that I have yet to find any kind of a code solution that in addition to changing the hue around the circumference of the circle, also increases the value (brightness, HSV color model) as you approach the center of the circle. One can imagine nesting many rings inside each other to to create the desired effect, but that seems like a lot. Is canvas the best approach here? I don't know.~
It should be possible to generate the color gradient somehow. Adobe does this with a canvas. This open source project has accomplished this feat: iro.js
~The problem is that I have yet to find any kind of a code solution that in addition to changing the hue around the circumference of the circle, also increases the value (brightness, HSV color model) as you approach the center of the circle. One can imagine nesting many rings inside each other to to create the desired effect, but that seems like a lot. Is canvas the best approach here? I don't know.~
Additional related examples: