Interior painting jobs vary in price depending of color chosen in comparison with the existing colors.
To cover a dark color with a lighter color will take several coats, including priming before painting.
Another variation can be the sheen, from flat which is the most common for walls, to semi gloss that is used to trims, bathrooms and kitchens, to high gloss that is most commonly used to cabinetry and fine furniture.
As long as you choose the same colors, even the sheen is different, the price doesn’t change much.
But as soon as you use different colors in the same rooms, takes more time and; therefore, more money.
The variations of color, sheen, paint grades and chemical composition can make a difference when it comes to price.