you reminded me now a feature from zx-spectrum basic - colours 0 to 7 you have all those 8 colours (ula hardware related) - colour 8 is transparent, and colour 9 is contrast (basic interpreter related) -
https://worldofspectrum.org/ZXBasicManual/zxmanchap16.html - colour 0 is like, when the paper is between 0 and 3 (black to magenta), ink 9 means it's always 7 (white) - when the paper is betwen 4 and 7 (green to white), ink 9 means it's always 0 (black) - colour 9 close to assure you will get over 50% of luminance contrast (a contrast often mentioned in Johannes Itten book The Art of Color ) - blue on black you get around 10% of colour contrast or less (perhaps about 7% because it's bright 0, i think - but it's not that problematic since the text you used is quite large) - anyway, i confess i use to have the monitors not that bright, my eyes get tired quite easily