What's the noun for rednesses? Here's the word you're looking for.
red
(countable and uncountable) Any of a range of colours having the longest wavelengths, 670 nm, of the visible spectrum; a primary additive colour for transmitted light: the colour obtained by subtracting green and blue from white light using magenta and yellow filters; the colour of blood, ripe strawberries, etc.
“The reddishness of the unglazed portion of the dish is characteristic of early Ming porcelain.”
“Reddishness around the sponges directly indicates the richness in the vascularization which correlates with the ability of SaOS2 cells to form solid tumors on CAM within 96 h of incubation.”