- This simulator by Andrew Duffy overlaps blocks of color, with adjustable sliders to illustrate additive and subtractive mixing.
http://physics.bu.edu/~duffy/HTML5/color_mix.html
- This simpler one by Tom Walsh offers three draggable circles of color, with sliders to vary the intensity of each.
https://www.ophysics.com/l1.html
- This applet by John Welch presents a challenge for students: match colors by simulating color mixing on an electronic display.