Individual pixels of white, red, green, blue, yellow, cyan/aqua, magenta/fuchsia
on a field of black in an uncompressed PNG file.
Use a jeweler's loupe to resolve the R G B components of the pixel triad of your monitor.
Set screen resolution to native resolution mode to avoid interpolation effects.
Ensure image is at its actual native size of 218x130.
"Blow-up" of the image's colored pixels:
Each pixel is a "triad" of three R G B components, roughly corresponding to
the long (reddish), medium (greenish), and short (bluish) wavelength cone
receptor cells (6M of them vs 92M rod cells) of our primate's trichromatic eye.
Each component is represented by one byte (8 bits) indicating the intensity/brightness
of that color (0 is off, 255 is full intensity). Each pixel is three bytes (24 bits), so it can be any one of 224
= 16M colors.
10,000 white pixels:
Computer screen is typically one of these (or larger):
width×height = the number of pixels.
There is no yellow light here:
The screen is emitting only red and green light at each pixel.
Your eye and brain, i.e. your mind, is creating the "yellow".