This is actually a biological phenomenon that most humans experience! Our eyes are more attuned to greens and blues rather than reds, so green and blue light appear brighter as the cones in our eyes are more sensitive to those colors. Similarly, our cones are less sensitive to red so it appears darker.

There's also a physics component to this as well since red light has about half the energy (twice the wavelength) as blue light. However, since there's a difference in energy, the engineer must take that into account when designing multicolor LED applications so as to keep a level light intensity when changing or blending colors.

Here's an eli5 question with some more info: https://www.reddit.com/r/explainlikeimfive/comments/ghx9g6/eli5_why_does_red_light_seem_darker/?rdt=58820