Customize the color of the chip icons separately from the text label

[lynnmercier]

Still deciding if --leading-icon and --trailing-icon should be the same color...or if we should also allow clients to customize them separately

[mgr34]

Perhaps a separate issue, but I believe the SASS mixin mdc-chip-fill-color-accessible should decorate the --[leading|trailing]-icon. For example if you were to call mdc-chip-fill-color-accessible(navy) the chip text color will appropriately become var(--mdc-theme-text-primary-on-dark,white) But the icons will not be accessible. Their color contrast is to low.