feat(avatar): updated colors

[agliga]

Fixes #2204

• This PR contains CSS changes
• This PR does not contain CSS changes

Description

• Swapped colors with new colors

Notes

• Since there is no official colors yet, I added them as private less variables (prefix with underscore). This way when we get the new colors we can remove them and it won't be breaking.
• Since these did not have any dark mode variants these are the same colors used in dark mode.

Screenshots

Checklist

• I verify the build is in a non-broken state

• I verify all changes are within scope of the linked issue

• I regenerated all CSS files under dist folder

• I tested the UI in all supported browsers

• I did a visual regression check of the components impacted by doing a Percy build and approved the build

• I tested the UI in dark mode and RTL mode

• I added/updated/removed Storybook coverage as appropriate

[ArtBlue]

Looks good