There are a few potions that are always the same color. Namely potions of water/unholy and holy water. These are all clear. And they are holy/unholy depending on their blessed status. They can be ID'ed by normal altar ID.
There is a table of potion probabilities on the nethack wiki. But probabilities range from around 1% to 7% so it isn't a lot of help.
The best way to determine potion ID is by first dipping a unicorn horn in the potion. This transforms a certain amount of bad potions into harmless ones.
The final thing you can do to ID certain potions is to use a amethyst stone. It turns potions of booze into potions of fruit juice.
Most potions have unique messages when you drink them. You probably want to use spoilers to get the messages.
One more thing, from the wiki:
Smoky and Milky Potions are special. A smoky potion has a chance of containing a djinni, while quaffing a milky potion may release a hostile ghost.
This can be pretty bad if your potions of extra healing are smoky or milky.
Get a unicorn horn, dip the horn in all the potions, drink the ones that do not change to ID them.