How to define class name with color code

I used to be quite confused when naming elements by color code.

Example issues:
This panel default has a background white
<div class="panel">default</div>

This panel default has a background #757575
<div class="panel panel__???">#757575</div>

This panel default has a background #cdcdcd
<div class="panel panel__???">#cdcdcd</div>

OMG! How do I name panel__??? class elements

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I recommend https://colors.artyclick.com/color-name-finder/ it solves naming

This case:
This panel default has a background #757575
<div class="panel panel__???">#757575</div>

Solved:
you can reference Name or Similar names
results
<div class="panel panel__boulder">#757575</div>

Link:
https://colors.artyclick.com/color-name-finder/