"I say my synethesia is mild because the colors are mostly faint."
Hmm, for me the colors are very vibrant when visualized in my mind. When I read black letters, the letters are clearly black, but there's a sixth-sense haze about them that is colored a certain way. I suppose you could consider it faint for me in that respect.
"For me, I see each letter's color, but the color of a word is mostly from the leading letter."
Yes, it's the same for me... However, there are some occasions like a double-e where the orangeness of the ee stands out more than the leading letter.
"Or, I confuse 4, 6 and 9, because, for me, they are all the same shade of yellow."
This makes me quite thankful that all my numbers are different colors... Looking back on your list, I am struck by the fact that most of your characters are some shade of the yellow-tan-brown spectrum. I suppose I have a couple greens, but you have a considerable number of yellows.