Would it be possible to add a gradient creation tool? Maybe like a panel to define gradients which could then be selected in the color tool? Here's what the panel could look like:
Type would give the user the option to have either a linear or a radial gradient.
Steps would be a table where the user picks the progress percentage, color, and opacity.
Defined would be a table that shows a preview of the gradient in a cell. Gradients are added from a button above that creates the gradient specified in the steps.