Checkbox icon for "checked" state in default themes is confusing

Environment/Versions

• GIMP version: 2.10.34
• Package: Built from source
• Operating System: Linux

Description of the bug

In the default (Light/Dark/Gray) themes, the icon for checkbox widgets in the "checked" state has an "X" mark in the checkbox. This icon has an ambiguous meaning, and can be interpreted to mean "disabled" or "inconsistent" rather than "active" or "checked". (The Dark and Gray themes make this worse by dimming the text next to a checkbox when the checkbox is checked, further suggesting that the "X" has a negative meaning.)

Anecdotally, since upgrading from GIMP 2.6 this has repeatedly confused me, to the point that I locally replaced the "X" icons with checkmark icons in the installed themes.

Reproduction

Is the bug reproducible? Always

Reproduction steps:

1. Select a tool with checkbox options (such as Pencil).
2. Toggle a checkbox option (such as "Apply jitter") so that it is in the "checked" state.
3. Observe the icon.

Expected result: The icon should clearly indicate that the checkbox is checked (such as with a "check" icon).

Actual result: The icon has an "X" icon, which can be interpreted to mean "disabled" or "inconsistent".