Background color and ink saturation

To print white letter, background color should be saturated. Another overlap test result:



I printed the same pattern (three color belts) twice with 90 degree rotation.

The belts are M100, C20 and C20M100 each (generally. My printer is home/office model, the so-called RGB printer. Cannot control ink by CMYK). M100 x M100 square shows little difference. This is because M100 is nearly saturated. M100 x C20M100 square is the same thing. C20 x C20 shows distinct difference. Because C20 is far from saturation.

C20M100 x C20M100 square shows, not very distinct, but noticable difference. It's because C20 ingredient is not saturated.

In the conclusion, every ingredients of the background color should be saturated.

In that case, background color is restricted to these colors at most?
CMYK
Light Cyan
Light Magenta
Light Black
Light Light Black
...and mix of them
(But I doubt that the light colors are simply diluted)

In some way, yes. If I can get spot color ink for dye-sub, the answer is no. But I couldn't find such thing yet.

But...

C20M100 x C20M100 overlap is not seriously noticable. It's OK if overlap is narrow enough.

(C20 background is impossible though, any way)