well I am no expert and this may seem crazy to the pros but I think of "normal" as more like a combo co dom morph then a dom. or ress. gene type, there are many genes involved to make a normal, several that make up pattern and seveal more that make up color varietys. If any of these change its not a noraml any more, even though most of the genes are still normal.
womaXenchilXspiderXPintstripe, never seen one just made it up for an example , Enchi is a normalXEnchiXnormalXnormal, a spider is NormalXNormalXSpiderXnormal and so on. In short I think of Normal as just the naturally selected Multi-Gene morph, see normal as normalXnormalXnormalXnormal, But thats just me:)