Add option to lower the text's contrast

[BloodyHazardous]

Being able to change the colour of the text would benefit me personally, recently reading has become a pain, due to increase light sensitivity, reading white writing on a dark background causes eyes issues, irritation. Its the contrast between light and dark. And due to this being a program and not a webpage there's not much i can do,

[NathanLovato]

There's now an option for the main text thanks to #689. We're missing the code's colors to complete the feature. But this should already be easier on the eyes for most of the app's text.

[russeg]

Not sure why this is the feature, since what should be implemented is Light/Dark theme switch.

Light mode should be the default, and dark an option since dark mode is actually an accessibility problem.