fix colors on various modals provided by Chromium

[LaurenWags]

Description

The colors on the "Make Brave Faster" modal look more "Chrome blue" than "Brave blurple". They should be updated to match our coloring.

Steps to reproduce

Not sure how to reproduce, just stumbled across the modal/notification

Actual result

This is on dark theme, not sure if the same colors apply to light theme

Expected result

Colors should be more "Brave" less "Chrome"

Reproduces how often

Easily reproduced

Brave version (brave://version info)

Brave	1.69.147 Chromium: 128.0.6613.40 (Official Build) (x86_64)
Revision	d29b1747d0f906239936b0d94c40889920ebf2c0
OS	macOS Version 13.6.9 (Build 22G830)

Channel information

• release (stable)
• beta
• nightly

Reproducibility

• with Brave Shields disabled
• with Brave Rewards disabled
• in the latest version of Chrome

Miscellaneous information

cc @rebron @mkarolin

[LaurenWags]

Saw on another modal with 1.72.6 Chromium: 129.0.6668.42, no idea how this modal was triggered though. It doesn't look Chrome blue but it does look odd.