Ensure Button label renders as correct light/dark color on primary + color Button

[taysea]

<Button color="purple!" label="Feedback" /> 

renders with "black" text instead of previous "white" -- this is due to recent theme changes related to desired primary button label color when background is HPE green vs other colors.

The theme should:

1. Use text-primary-button when the primary Button is HPE green.
2. Leverage button utils to determine which label color should be used when Button has primary and color applied instead of keying off of theme mode.