Color stimuli
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The following parameters can be used with "stim_form 3c" to
convert a grayscale '3d' stimulus into a color ('3c') stimulus:

* **color0_r** - red component of color associated with amplitude 0
* **color0_g** - green component of color associated with amplitude 0
* **color0_b** - blue component of color associated with amplitude 0

* **color1_r** - red component of color associated with amplitude 1
* **color1_g** - green component of color associated with amplitude 1
* **color1_b** - blue component of color associated with amplitude 1