Branch indicators lack contrast

[marijnvdwerf]

In light mode, most branch indicators don't contrast enough with the background.

Also, the colours seem pretty basic (#fof and #0ff) and all over the place, it might be interesting to look into adopting some predefined palette. Some common datavis palettes can be found at https://plotly.com/python/discrete-color/#color-sequences-in-plotly-express.

Example:

Constrast values: (counting everything below 3.0 as a failure, though this should probably be more like 4.5)

[mkst]

Is this a duplicate of #https://github.com/decompme/decomp.me/issues/678 ?