Synesthesia is when numbers and letters of the alphabet have their own colors. The parts of your brain that control language and color are crossed (if I remember it right.) There are more examples of the different types of synesthesia but that one is the most common (and the one that I have.) So say I'm looking at a newspaper; I can see that the letters are black but to me, they each intrinsically have their own colors. Some letters are darker than others. Some letters really stand out. (Especially pink.) So here's my list of what I see:

Numbers:
1 off white/light yellow
2 yellowish (but not yellow) pinkish (but not pink) and not quite orange either
3 tan
4 sort of a blackish dark purple
5 red
6 pink
7 green (a lighter green than 9)
8 blue (a slightly dark blue.) P.S.--I extremely dislike number eight.
9 dark green

Alphabet:
A pink
B brown
C yellowish orange
D dark black with the presence of purple
E sort of blue but seems like it should have some black and or grey
F black with maybe some blue or purple
G green
H red (but has the slight presence of brown)
I white
J grey
K red
L yellow
M sort of red brown
N yellow-orange
O white
P purple
Q grey
R black with ...grey? blue? slight purple?
S pink (magenta)
T green
U yellow
V grey-black
W dark purple
X black
Y yellow
Z grey-black