Text Fields - changing the background colour - problem on a Mac

I did not have this problem on a PC !!

I want to change the colour in a Text Field. If it is preset as transparent like this

and I try to change the colour - notice that the fill colour on the right has a greyish colouring

I click the exit red button and nothing changes. Same problem with the border colour.

The same in reverse. If I reuse an old field which had a coloured background I cannot make the background or border transparent again.

I have spoken to Support - who tried everything including the tried and tested uninstall and reinstall but no success.

Strangely a colleague of mine (with a Mac book) has an extra box for ¨transparency¨ which is not on mine. Maybe it only for the French  ... Mon Dieu ?

Is this a setting problem  ??