Each marble's colour shows its own speed — that's what a single atom actually has. Temperature isn't a property of one atom; it's the average speed of many atoms in the same region. The °C ticks on the legend are the temperature you'd measure if the whole gas were at that speed.
In a gas at any single temperature, individual speeds follow a Maxwell-Boltzmann distribution — a wide bell curve of fast, medium, and slow marbles all present at once. About 5% of marbles are momentarily above 3× the average speed, which reads as "hot" on the palette even though the gas overall isn't. To keep the eye from being dazzled the renderer smooths each marble's v² over about 30 steps so it shows the marble's local speed, not thermal noise.
The region labels (indoor air: X °C, refrigerant: Y °C) are means over many marbles — those are real temperatures.