WIP--Tidewater Cardigan, a sleeve, still a sleeve

Behold, my first sleeve is (still) coming along:

I think the variegation looks better this time around. But now the only question is whether I should slowly add in one of the blue skeins? How much yarn does it take to do a cardigan? I have no idea. Because if it's 300 grams (or, 1260 yards), I'm fine and I don't need that blue skein. But if I need more, I should start adding now. So how do you know?