invert text in dark spots when not coloring background

[deathtrip]

When you use the -i option to color the background, letters that could blend with the background color are inverted, so they can still be visible.
This isn't the case when the background isn't colored, so some parts of the text can become invisible.
For me it happens with a black background and the darker gradients like magma or inferno, which can have black spots.

[mazznoer]

The problem is terminal background can be anything, dark, light, image, transparent, and we can not know what color is under certain character.

[deathtrip]

Maybe a command-line option to tell lolcrab the background color?
Most people use single color backgrounds, and with images or transparent, fading shouldn't be such a big problem.