Photoshop Transparency Background Showing Blue - Help!

Hi all,

I was hoping I could hive mind the Adobe forums to see if anyone understands the issue that I'm currently having (Photoshop CC v. 19.1.9)

For some reason, my transparency background tiles are showing as shades of blue. When I go into Preferences > Transparency & Gamut the grid colours are showing as two shades of blue (although I swear when I first opened this preference box when having this issue it was showing as grey and white) yet the preview box shows as grey and white.

If I change the custom colour values to grey and white the preview shows yellow, and actual background goes a different shade of blue.

It doesn't seem to be affecting the colour values of other layers (eg. the white rectangle) although I was having issues yesterday with trying to use curves to make an image 100% K so not sure if that's related.

Please see below two screenshots of the variations of this issue.

Any advice is hugely appreciated

Beth