Refactor: Replace static hex values with design tokens in test files

[theceo1]

Description

Replaced static hex color values in test files with appropriate design tokens from @metamask/design-tokens to ensure consistent color usage and alignment with the design system.

Related issues

Closes #14299 (or the relevant issue number, if applicable)

Manual testing steps

1. Run yarn jest app/components/UI/Ramp/components/PaymentMethodSelector.test.tsx
2. Confirm all tests pass for the modified file.

Screenshots/Recordings

N/A

Pre-merge author checklist

• All hex values in test files replaced with design tokens
• All tests passing for changed files
• No eslint warnings for @metamask/design-tokens/color-no-hex rule

Pre-merge reviewer checklist

• Code follows project conventions
• All tests pass
• No regressions introduced

[github-actions]

CLA Signature Action: All authors have signed the CLA. You may need to manually re-run the blocking PR check if it doesn't pass in a few minutes.

[theceo1]

I have read the CLA Document and I hereby sign the CLA