tweak(base): re-balance symbol-overlay colors to improve visibility

[jimeh]

Minor tweaks to colors so they're all more balanced, and a little bit more visible across different themes. Some colors are still slightly less visible on some themes compared to others, which I see no way around without having per-theme specific colors.

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• I searched the issue tracker and this hasn't been PRed before.
• My changes are not on the do-not-PR list for this project.
• My commits conform to the git conventions.
• My changes are visual; I've included before and after screenshots.
• Any relevant issues or PRs have been linked to.

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After @seagle0128's comment I took a closer look at how the different colors I had picked in #750 appear on a long list of different themes.

The result is the subtle tweaks to color blending values in this PR, which I feel are overall a reasonable compromise to look good in most themes. I would not call it perfect in every theme, but more than good enough in my personal opinion. I'd be happy to adjust further if people disagree with my opinion though :)

I might have gone a little overboard, but below are a series of before/after screenshots for how this PR affects the various symbol-overlay-face-* faces across a bunch of the themes.

Screenshots

doom-one

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doom-one-light

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doom-vibrant

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doom-dark+

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doom-molokai

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doom-monokai-classic

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doom-monokai-pro

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doom-nord

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doom-nord-aurora

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doom-nord-light

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doom-nova

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doom-solarized-dark

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doom-solarized-light

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doom-solarized-dark-high-contrast

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doom-tomorrow-night

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doom-tomorrow-day

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doom-zenburn

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doom-dracula

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doom-Iosvkem

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doom-opera

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doom-opera-light

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``

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[seagle0128]

@jimeh Thank you for the tweaking! I think you should also check the highlighting other words of different foreground colors.

[jimeh]

@seagle0128 Ah, yeah good shout. I knew I should have finished my coffee before doing this 😅

[seagle0128]

@jimeh Any update for this PR? And I still think the colors should be lighter. The foreground colors of the characters may be very close to the background colors. The default faces of symbol-overlay are very clear and obvious. I think user experience is better.

Please the screenshots below.

My tweaks:

[jimeh]

@seagle0128 Sorry for the silence, I'm gonna try to get back to this in the next few of days.

I agree with you and prefer the tweak you've done to what's in here right now.

My plan is to try a few different variations of background/foreground color combos across a whole bunch of the themes, and grab screenshots of it all to post here for comparison :)

[seagle0128]

@jimeh Thanks! Please proceed as your plan...