Make refine-bravais table colours easier to read (+for colourblind)

[ndevenish]

As well as the whole red/green issue we discussed the red is very intense and makes it hard to read. When we discussed this, we talked about possibly making it a more muted/desaturated red And this is what I meant:

Which is higher contrast and easier to see the N, even without the colours. Perhaps do the same thing for the green.

Other options include patterns but without the low-contrast conflict between text and background the letter might be enough.

[dagewa]

For example, simply changing this line:

                    item.setBackground(Qt.red)

to

                    item.setBackground(QColor(255, 0, 0, 127))

produces this result, pretty similar to @ndevenish's example:

It would be better to specify a set of DUI colours rather than instantiating each time, of course, but essentially this is a trivial fix! Adding to high priority now because it is a year old but is easy.