Well, pronunciation, definitely. Brits are very non-rhotic (meaning, "dare" sounds more like "day-uh"), yet they manage to sneak in an extra R where there wasn't one previously (that pesky "intrusive R," as in "that cheetahR is so fast"), they pronounce voiceless stops "properly" (for example, "water" is actually "wah-ter" - or rather, "wah-tuh" - for them and not something like our "wah-der"), and "h" seems to always be pronounced ("herb," for example).

Spelling is another one, like you mentioned. That's actually due to Noah Webster, of "Webster Dictionary" fame. He decided that America needed to feel like its own separate nation in order to weather the wars against the British, and to do that, the language must be separate as well. He threw out a lot of the spellings that tied us to our Norman/French heritage ("theatre," "colour") in favor of spellings that mirrored current pronunciation at the time ("theater," "color").

Then there's vocabulary - the obvious ones being lift/elevator, boot/trunk, football/soccer, university/college, lorry/truck, chips/fries, crisps/chips, biscuit/cookie, maths/math, and the ever-popular rubber/eraser ("May I borrow your rubber?" "... Ew!"). There's tons more, of course, but those are just some off the top of my head. There are way more at the last link in my sources.

As for verbs, Americans tend to use "got" as a catch-all past tense form, whereas Brits prefer the "have" form. I notice, too, that Brits tend to word their past tense differently, like "I've not been there yet," whereas in American my instinct is to say "I haven't been there yet." There's also the peculiar usage of "I'm in hospital" that Brits use, whereas Americans would say "I'm in the hospital" or even "I'm at the hospital" (or, more descriptively, "I'm dying, come quick").

And that's just listing stuff off the top of my head. There are so many interesting (yet overlooked) differences between the two dialects. The first link in my sources is a fantastic overview of all those differences.

Now the big question is, will we one day suddenly realize there have been too many differences piling up between the dialects and now we can't understand each other? :)

The ones you mention like color affect me a lot actually. I use different spellings depending on context now.

The one case I find most interesting has come up a number of times when interviewing and hiring people.
The word is "quite" when used in the context of "They are quite good at what they do"

In American English quite tends to mean "not as good". So the sentence would be generally interpreted as "They are not as good as you might expect them to be"
In British English the qualifier means "better than" so the statement might be interpreted as:
"They are better than you might have thought they would be"

Needless to say - when offering a positive review of a candidate to an American - they interpret as a disappoint review. Which can lead to serious misunderstandings...

The pronunciation is same but spelling is different. For example, Colour-color and few words are varied in normal conversation. You can get help from private tutors of tutorz site to write/speak American English.

The main difference notice between American English and British English in everyday writing and speaking on the following basis:-
1.Vocabulary
2.Nouns and Verbs
3.Spelling

1 Vocabulary-There are difference on the basis of vocabulary for instance americans would refer to as an elevator,
and on the other side the bristish would call a lift.Both groups are refering to the same object
but both are using different word to describe the object.

2.Nouns and Verbs
There are difference on the basis of nouns and verbs:-
In British language collective nouns can be used with singular or plural verb forms.
In American language collective nouns usually use a singular verb form.

3.Spelling
There are difference on the basis of spelling in American language words end with letters 'ze' and on the other side in British language words end with letters 'se'.
An example would be 'analyze' American and 'analyse' British.