It is looking to me as if the two different yarns used are different weights.
I used this chart, but as you will see, the first of the yarns, the "Germantown" was produced in different weights, and unfortunately none of them match the exact name given in the pattern!
www.purplekittyyarns.com/discontinued-yarn
The first yarn (white) looks as if it might be DK or even slightly thicker. I can't find the exact one, but I think this might be similar: Bear Brand Ever-Match Nylon & Wool Germantown - 120 meters per 2oz skein
But the second yarn, the 'color', is lightweight: Bear Brand Pompadour - 220 yards per 1oz skein.
If I am right, I suppose you would need roughly between 250g - 300g of the thicker yarn, and 100g of the thin one, but please wait for someone else to either confirm or correct that before you commit to anything.