Sumatra PDF is a PDF, ePub, MOBI, CHM, XPS, DjVu, CBZ, CBR reader for Windows

High brightness (or contrast)

So on version 3.2 the document files are too bright. Also the background color is much whiter than in 3.1.2, it makes pages barely distinguishable from the background and it is hard to read the text.

There may be very slight differences within images due to improvements in MuPDF color tone rendering. So for example the greens may in a few cases be a percent difference.

100% Black is still 100% Black and 100% White is still 100% White, there can be no difference in contrast between 3.1.2 on the left and 3.2 on the right when both are on the same screen.