capital or lower case after colon

The word "never" should start with a lower case 'n'. It is not starting a sentence.

Thank you very much, Contrex, for helping me frequently.

depends on whether the following is a complete clause or not, a capital for the complete clause, lower case if not.

in your case use a lower case

Kuvasz described the US English practice. In British English, which I believe Tanguatlay wishes to follow, the word following the colon is NOT capitalized unless it is a proper noun, an acronym, or if it is normally capitalized for some other reason.

Thanks, Kuvasz and Contrex.

I don't know why AmE often has different versions from the BrE.