Suboptimal interaction between black-on-transparent images, white page backgrounds, inversion theme

[the8472]

without owl: black-on-transparent on white background -> black on white

with inversion theme: black-on-transparent becomes white-on transparent on white background, then gets inverted again -> black on black

This is an issue with diagrams, icons, rendered latex and similar in SVG or PNG.

Possible solutions:

• option to put a white background under images
• detect such cases (pixel sampling with canvas) and skip inversion

[YangVincent]

If it were possible to detect these (especially latex) and render them as images, that'd also work.