Anywhere in the blue is the best answer the scanner can give. Shades aren't indicative of signal density, but of the underlying terrain.
As you get lower, you can toggle the cockpit between modes so that you see the actual planetary surface underneath. Is the bit you're aiming for very rough and rugged? Pick a different shade of blue to aim at. Even if you do find things in the rough terrain, getting to them is such a major pita I can't recommend it. It's also fairly rare to find biology in the extremely rough terrain, it usually prefers the smoother flats. Notable exception being osseus, which seems to like hills. Geology is fairly evenly distributed; it's more a matter of inaccessible hills than it not being in there.
Also; be aware that you may get unlucky. Some planets have very sparse geology or biology, others are rich with it. If you feel like you've come down in the blue and there's nothing here - you might not have done anything wrong! Sometimes you just have to shrug and move on when your triple geo planet just doesn't seem to have any. The next one likely will