[Suggestion]: Use OKLCH instead of rgb(a)

### Summary
OKLCH is starting to get traction because it provides a better way to define colors. It also improves a11y.

### 💬 Description
Here's a list of links to read up on OKLCH:
- https://uploadcare.com/blog/oklch-in-css/
- https://www.smashingmagazine.com/2023/08/oklch-color-spaces-gamuts-css/
- https://evilmartians.com/chronicles/oklch-in-css-why-quit-rgb-hsl
- https://chriscoyier.net/2023/05/25/two-things-that-are-not-great-about-oklch/

### 💰 Use value
Make the ic-design-system top notch with modern practices.

### 📝 Acceptance Criteria

*Given* the designs and color palettes in ic-ui-kit
*When* oklch is implemented
*Then* dx/ux and a11y is enhanced

### ✏ Designs

N/A

### 🧾 Guidance

See above

### 🚨 Urgency (low, medium or high)
not time sensitive (low)

### Additional info
N/A

Start by reviewing the designs and color palettes in ic-ui-kit, then read the linked OKLCH references to understand the proposed direction. The issue names no files or tests; done means OKLCH is implemented for the relevant palettes with the stated DX, UX, and accessibility improvements.

Written by the indexing model from the issue text.