Truly isn't NASA the sole space agency to have explored Mars. During the Space Race, the Soviet Union had a few probes sent themselves to Mars. I'd recommend checking out through this exclusive catalog of Soviet Mars images. In modern times, however, we got Mars Express lead by ESA, which is completely independent from NASA. Now, why pictures of Mars is often represent with color inaccuracies isn't exactly a part of a secret conspiracy that wants us to think Mars is literally a red rock. Ezer has already given us a basic explanation, but still, it's often space agencies are using a red color filter when taking pictures of Mars – and with a good reason: It's a technique used to increase contrast and bring out terrain features that might had otherwise been hard to distinguish. In fact, Amateur astronomers are doing this themselves.