"Create a sticky (…) Ctrl + Shift + C" is the combination used in Mozilla Firefox for Developer Tools.

Text in predefined fixed colors is hard to read in most cases:

Foreground: #FFFFFF
Background: #5AA885
Contrast ratio: 2.848: 1
1.4.3 Contrast (Minimum) (AA)
Fail for large and regular text
1.4.6 Contrast (Enhanced) (AAA)
Fail for large and regular text

Foreground: #FFFFFF
Background: #4DD35C
Contrast ratio: 1.947: 1
1.4.3 Contrast (Minimum) (AA)
Fail for large and regular text
1.4.6 Contrast (Enhanced) (AAA)
Fail for large and regular text

Foreground: #763A37
Background: #FF5D54
Contrast ratio: 2.858: 1
1.4.3 Contrast (Minimum) (AA)
Fail for large and regular text
1.4.6 Contrast (Enhanced) (AAA)
Fail for large and regular text

Foreground: #FBDCF4
Background: #F235C7
Contrast ratio: 2.725: 1
1.4.3 Contrast (Minimum) (AA)
Fail for large and regular text
1.4.6 Contrast (Enhanced) (AAA)
Fail for large and regular text

Foreground: #EEF5FC
Background: #2689DE
Contrast ratio: 3.342: 1
1.4.3 Contrast (Minimum) (AA)
Pass for large text only. Fail for regular text
1.4.6 Contrast (Enhanced) (AAA)
Fail for large and regular text

Foreground: #76502E
Background: #FE963C
Contrast ratio: 3.26: 1
1.4.3 Contrast (Minimum) (AA)
Pass for large text only. Fail for regular text
1.4.6 Contrast (Enhanced) (AAA)
Fail for large and regular text

There is no way to use the extension to set a color flag for web pages via the extension button indicator color. That is, it is enough for me to see that I previously set the current page to "red color" or "green color", without adding any elements to the page itself.