The first specification said #0B0D10 with a #4C8DFF accent. Both were wrong, and I wrote them myself.
Pure black plus a saturated blue is the prop-firm formula — it reads as application chrome no matter what else the page does. The ground is now #101214, lifted just enough to read as a surface being printed on rather than a screen being operated, and the accent is desaturated to #6E93B8. My own test for the whole design was whether I would feel I was about to open a trading platform. Two hex values decided it.