Either color or "classic" should show you suspended fish, at least if the calibration or sensitivity is dialed in right. I understand that the biggest advantage to the color sonar is to see the type of bottom. You can really tell the difference between sand, shell, or rock - much better with a color unit.
Of course, mine is B/W due to budget concerns, but when looking for fish I like to keep it on "Dual-display" where it shows the 50 and the 200 kHz views side by side. That way I see all of the fish that aren't biting.