In my word processor (MS Word) both spelling and grammar can be checked "on the fly" as you type.

While I do use the spell check occasionally for words about which I suffer from "temporary uncertainty" I find that usually the "grammar check" is simply wrong, so I ignore its suggestions or just turn it off most of the time.

Fortunately there is the additional feature called "autoreplace" and since it executes after the spelling and grammar checks it can be easily used to override errors in the prior functions.

An automated feature to detect "caps lock errors" automatically changes upper case characters to lower case unless they follow a period (full stop) and space. This makes it impossible to type a number of "corporate names" that mix upper and lower case in the same "word." You can, however, put the correct typography into the autoreplace as "always replace" [whatever the spell check wants] with [what you really want] so that it will be automatically changed back after the checkers have changed it to wrong.

In the case of color vs colour, if you put "always replace color with colour" into the automatically replace as you type function, you should never see the "spellchecker's" incorrect correction again. (If your word processor includes the necessary smarts.)

The effective use of these functions is significantly more difficult in newer versions of Word (2007 and later) but that's just because Microsoft is adhering to its new motto "Only Idiots will buy our stuff" and have dutifully removed or hidden/obscured anything that someone who isn't an idiot might use. You can work around some of it.

John