Does and dose, than and then, lose and loose, there and their, to and too...are they that difficult?

English is my third language (Italian and French are my first and second, Welsh is my fourth) and I have got pretty good grammar. I personally can't understand American English very well, becsue even though I know the differences, they always throw me off. For example, meter rather than metre or color rather than colour - it is very confusing when you've learnt the proper spellings, to then be faced with a load of variants. I can deal with mutations, because Welsh has lots of them. There is no rule to American spelling though - it's completely random.