When Stealth Fails, Try Boldness

Why camouflage?
For most of human history, camouflage was not used in organized warfare. Today the benefits of camouflage seem obvious, but in the past the lack of it made just as much sense. In warfare, posturing is just as important as killing power. To win, you don't necessarily have to kill the other guy, you just want him to be so scared of you that he doesn't want to fight at all (If he doesn't run/surrender, then you kill him). To look scary you wanted to be noticed--you wore flamboyant costumes in bright colors, waved huge flags and banners to rally your troops and strike fear into your enemies. You wanted to be seen and feared, because fear was your ally. (e.g., "The Redcoats are coming!")

Reenactment of the Battle of Lexington, April 21, 2008 ¹The situation changed when weapons became so long-ranged and deadly that posturing in this manner was no longer effective. (Posturing is still around in modern warfare; it just takes on different forms.) Standing proud and tall in your bright uniform isn't as scary when the enemy can kill you easily from hundreds of yards away. Nowadays it is better not to be seen at all than be a tempting target.

To the Space Marine, camouflage is for wimps, while for the Imperial Guard, it's a matter of survival. But it was not always so.
Space Wolves on a covert mission ²In the old days of the 1980s, Space Marines made as much use of camouflage as did the Imperial Guard.

"Some Marine chapters adhere rigidly to the traditional patterns. The chapter of the Red Scorpions not only sticks strictly to the lore of camouflage handed down from their original founding and embodied in the Codex Imperialis, but views any deviance from this practice as tantamount ot heresy ... The Commanders of the Imperial Guard are less stringent about such things than Marines, and will sometimes design their own schemes for a specific campaign." ³
Ultramarines Rhino in camouflage color scheme ⁴Later on the same article, the more "modern" view seems to apply:

"Many schemes show no attempt at camouflage as such, but consist of solid heraldic colours proclaiming the identity of the occupants as surely as the shield of a medieval knight. Indeed, there are some Marine chapters whoe tradition actually forbids the use of camouflage on the grounds that "the colours of cowardice" are wholly inappropriate to a true warrior. This attitude, although by no means rare amongst the Legiones Astartes, is not officially recognised and is not emboded within the ancient Codex Imperialis." ⁵

The current trend in 40k is that all Space Marines paint their power armor and vehicles in the chapter colors, regardless of whether those colors are vibrant or subdued. The reason for this is probably due to the fact that brightly painted armies just look fantastic on the tabletop. This is one of the compromises the hobby makes to improve the wargaming experience. Armies with well painted camouflage schemes may be more "realistic" and blend in with the terrain, but because of that, they aren't as aesthetic. Most players want to paint an eye-catching army, not a dull one.
My Brazen Claws, looking pretty on the tabletop
For my Tau army, I originally wanted them in a camouflage scheme, but I also wanted them to stand out on the table. I also used a limited palette of Jade Green, Vile Green, and Scaly Green (unfortunately all discontinued, although I have found matching colors from Vallejo Game Color paints). My reasoning behind the scheme was that the Tau had originally been fighting on an exotic world with Jade Green colored vegetation.

One of the problems with this scheme was that since the palette was limited, there was little contrast on the model, and with the camouflage pattern, the outlines of the various pieces were also blurred. In a sense, the camouflage worked, and the result was that while the model had a bold color, the details of the model were minimized and the result was somewhat bland. My new paint scheme is much bolder, with much more contrast, and the result, I believe is more attractive.

My Tau, with the old camouflage pattern on the left, and the new, bolder scheme on the right.

In my early days in the hobby I wasn't too keen on brightly painted armies, but since then they have grown on me. But is it possible to have an army in camouflage, and still have it look striking on the tablestop? I say yes, but I'll elaborate on that in another post.

Notes
1. Joanne Rathe, Boston Globe Staff, April 21, 2008.
2. White Dwarf, Issue 105, September 1988, illustration by Russ Nicholson.
3. White Dwarf, Issue 103, July 1988. Rampaging Rhinos, Technical Drawing by H, coloured by Colin Dixon and Sid, p65.
4. White Dwarf, Issue 105, September 1988. Land Raider!, Rick Priestley, p4.
5. Ibid.