The problem with "more red" is that it is ambiguous.
1. It can mean a % of the color rather than a comparison.
This new color is more red than orange. = It contains more red paint/dye/coloring than the amount of orange paint/dye/coloring.
2. This ripe tomato is more red than green. (70% red and 30% green)
"This ripe tomato is redder than that unripe tomato" is the correct way to compare.
The confusion may stem from the fact that we have heard "more read" in such sentences as "Wesley is more read than Walter Scott." And "more red" sounds just like "more read"