What is usually more expensive: anthracite inside + outside or only outside anthracite and inside left white?
As you already recognize yourself: "left" is the keyword for less effort.
Therefore, white inside should be cheaper because the plastic is white and does not need to be foiled.
That's right. Although foiling is not the only way to get colored window profiles, Gealan coats. With aluminum, both half profiles are coated separately, and thus with equal effort in different colors. Usually, white is priced the same as a whole bunch of colors.