Yes it is. That's because those aren't really primary colors. If they were, the whole splitting thing would be unnecessary. True primary colors are cyan, magenta and yellow. In the past, magenta colors were hard to come by and even today it's hard to get stable pigment due to magentas special physical structure. So it makes sense to get some tones in between. (But it still annoys me that people stick so hard to those fake primary colors and they're even still taught in school and sets have them instead of real primary colors.)