I couldn’t find any information online about how using a blue underpainting for a portrait was done, but I’m basing this off of what I saw Leo Stevens do while recreating Raphael’s “La Fornarina”. Leo used a green underpainting, and while I’m using blue, I copied his method of only putting it on the contours of the face. I did this over a grisaille.
In the later stages of painting this, I noticed that some of the darker parts of her skin had taken on a violet tone. I was puzzled as to what could have caused this, but I should have known that would be the result of glazing color with red mixed into it over something that was blue. Maybe next time, if I want to give someone a rosy glow, I'll add some yellow into the skin, or yellow ochre, if I'm glazing it over blue, to prevent the violetization of the skin. Yes, I just made up a word there.
If I was going to try this method again, I would not mix red directly with the flesh color, at least not for the parts I intended to paint over the blue. That’s how I got the violet. In doing this, I accidentally mixed a color by glazing. Mixing color intentionally by glazing can look beautiful, but it's kind of annoying when it happens against your wishes.
So, does using a blue underpainting give a more realistic result? I don’t think I can say conclusively yes or no. First off, it may depend on the subject’s skin tone. I have a feeling this technique works better on subject’s with lighter complexions. This was a renaissance technique apparently, and most subjects of paintings back then were Caucasian as was the subject I chose for my piece. In fact, the reason I specifically chose the subject I did is because she reminded me of someone who might have been in a renaissance portrait. The skin of Caucasian people is thinner than those of people of other ethnicity and so the veins tend to show more through the skin, which is where the blueness comes from. Extremely dark skin also tends to have a bluish cast to it, so this technique might also work if your subject has that type of skin tone.
Regardless of your subject’s skin tone, I believe glazing, ie, applying color in light layers, in this of the flesh tone over the blue, is the key to making this work. Surprise, surprise, glazing was also a major technique of the Old Masters.
So that is my experience doing a portrait with a blue underpainting. Here are some pics of the process.
Painter of portraits and wildlife