If you do dye them here is a formula I got from the web.

Well, I dyed my faded seat belts. They came out great. The formula my
wife
used as followed: four ounces of Rid dye in six qts. of boiling water.
Then
add one half cup of vinegar to the boiling water. With a wooden spoon
or
paint stirring stick sir. Then add the belts and stir every 5min. for
45
min. Remove from the heat and let stand for 8 hours. Remove the belts
and
rinse with a hose. placed the belts after thoroughly rinsing in a pan
with
laundry soap and wash. rinse the soap out of the belts and place the
belts
in a clean six qts. pale of water and and another half of cup of
vinegar.
Let this stand in the clean vinegar water for another 8 hours. Remove
belts
and let it dry in the sun. The vinegar is a must to keep the dye from
running. It sets the color. Gary P