If you have autocorrect on, and you override the correction a few times, it gets added to the dictionary, as far as misspellings go.
For names, if the name is in your Contacts you will not get spelling correction for it. You can use this trick for other words as well, if you don't mind have some strange entries in your Contacts.
Another thing that 'might' help is to add more dictionaries to the system dictionary. When you select a word and choose Define, there is a Mange option in the dictionary dialog. Downloading all three of the available English dictionaries should reduce the number of spell corrections, at least for things like color and colour. Or maybe not. I'm not certain the spelling dictionary and the system dictionary are the same, combined, or entirely separate.
There is no way, that I know of, to directly add words to the spelling dictionary. At least not on a stock iPad. I believe there was one for jailbreaking, but I don't know if that tweak is available for iOS 7 yet.