The red on the hull would probably have been Red Lead paint, an anti-fouling paint used on ships below the waterline. The color would (depending on where the pigment was mined) probably be approaching the red of the White Star Line Pennant. I don't know if Red Lead is still available or not. You would probably be fairly close going with the red on the QE II hull or the Queen Mary.
The white color on the superstructure should be like a piece of white printer paper, not the grayish color in your renderings.
"White Star Buff," your guess is as good as anyone's since, IIRC, no reference samples exist to be able to recreate it.
The black and white photos show that the colors on the Titanic appeared to be a gloss finish. That gloss is going to be difficult to reproduce, even printing on glossy paper, because of the degree of gloss or how glossy the item actually was.
There are a couple of other things to consider. The color you see will be dependent on how your monitor shows the colors. If the picture is printed, then it will also be a function of how well the colors are rendered on the printer (how well the printer is calibrated). I did a lot of photography, so I spent probably 8-10 hours calibrating my laptop monitor and the printer to get the color rendition as close to possible to the test images.