Lehto means "Grove".
If you mean dark hair, dark color or something like that, then it is "Tumma". Pronounced the same way as written. Dont try to pronounce the two m's as one, that sounds really really stupid, people...
The Finnish word for Christmas is Joulu.
You'd need a keyboard with umlauts, or you have to use unicode characters.
There are a few options. You could say kulta, rakas.