Is additive color mixing a linear process?

Is additive color mixing a linear process (or close to)?

(if this question has already been answered in detail, please forward me)

If the answer to this question is "yes" then:

Considering three hypothetical LEDs:

Red T-1 (650nm λ), 60° viewing angle, 1000mcd luminous intensity
Green T-1 (510nm λ) 60° viewing angle, 1000mcd luminous intensity
Blue T-1 (475nm λ) 60° viewing angle, 1000mcd luminous intensity

Point all three of these LEDs at a printed test pattern, the human eye and brain should see and interpret the printed test pattern illuminated with a patch of neutral white light. If additive color mixing falls with 1 - 2% of a linear model I would consider the process linear

If the answer to this question is "no" then:

The above setup would not create a patch of neutral while light. Different bands of color could exist as significantly more dominate than other bands of light. The resulting "white" light would be skewed in color and temperature if certain bands of light are more dominate than others.

Comments and links to other resources are welcome.
Reactor89