For example Ferrari have black numbers on a red background on their 2022 livery, and worse, some cars have stylised numbers that are almost illegible. It shouldn't take detective work to read the race number, they are supposed to be highly visible at speed for the purposes of (back-up) manual race timing (if required) after all!
Something along the lines of "Hindu-Arabic numerals must be used with sufficient contrast and legibility to be correctly transferred to text by [X] OCR software, when photographed at X mm distance using a Y mm lens with f/3.5 on a Nikon XYZ in a shaded pit garage" perhaps?
For reference, Google Lens refuses to recognise that number as text at all let alone as a 63! [Google Lens has no trouble identifying the "Right F" which is actually legible...]
I'm not sure I would want to go far as saying "you must have white or black squares of (say) 200x200mm with respectively black or white Helvetica numerals of no less than 150mm height" (as you might find in the regulations of say Formula Vee or Formula Ford), they can still have creativity and styling choices but with the rules as they are F1 livery designers really seem to be taking the mickey!