change: Tweak default light colour scheme

[ClementTsang]

Description

A description of the change and what it does. If relevant (such as any change that modifies the UI), please provide screenshots of the change:

Removes/tweaks some really light colours that might cause issues with a white background. For example, yellow on white didn't look so great, so I adjusted the memory/rx colours for this mode.

Issue

If applicable, what issue does this address?

Closes: #

Type of change

Remove the irrelevant ones:

• Other (something else - please specify) Minor colour scheme change

Test methodology

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Furthermore, please tick which platforms this change was tested on:

• Windows
• macOS
• Linux

If relevant, all of these platforms should be tested.

Checklist

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• Change has been tested to work, and does not cause new breakage unless intended
• Code has been self-reviewed
• Documentation has been added/updated if needed (README, help menu, etc.)
• Passes CI pipeline (clippy check and cargo test check)
• Areas your change affects have been linted using rustfmt (cargo fmt)
• No merge conflicts arise from the change

Other information

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