Spell check for British English incorrect.

[ChrisOsborne]

Revit is suggesting that "grey" is spelt incorrectly and should be "gray". This appears in Revit 2025 & 2026.

Other words (such as colour) don't incorrectly flag as misspelt.

[vitorbortoncello]

You might not be looking for a solution, but for anyone else reading this post: you can always add words to a custom dictionary or choose to ignore the misspelling