# Homework Help: Need help with colors

1. Sep 23, 2006

### dnt

i know its suppose to be an easy topic but it always confuses me. i can never figure out what color will be shown in different circumstances. eg. what colors are shown under ____ light? or if you reflect _____, so and so colors are absorbed and others are reflected. of if _____ is shined on ______ you will see ______. stuff like that. for any color(s).

and for complementary and secondary colors - all of that stuff. i just never know how to answer these questions and what colors do what.

is there a website that would help me understand how to solve and answer the color questions? something to get me started and clarify the confusing stuff. id really appreciate it.

2. Sep 23, 2006

### Chi Meson

How many colors are you asked to deal with? That is are you just concerned with the primary (RGB) and secondary (CYM) colors? (And then, of course W&B)

If so, then it is convenient to think of colored light as "+" colors, and solids as "-" colors. That is, yellow light is "+R+G" . Solid yellow is a filter that is "-B". Are you with me so far?

3. Sep 23, 2006

### dnt

not really. whats the difference between colored light and solids? i thought they were all "colors."

4. Sep 23, 2006

### HallsofIvy

It's the difference between "additive" and "subtractive". If you shine a red light and a blue light on a white surface you will see both colors "added". The color you get will be "lighter". If you shine a white light on a red painted surface, everything but red is absorbed ("subtracted"). If you use both red and blue paint, more of the white light will be absorbed and you will get a darker color.

5. Sep 23, 2006

### dnt

thats the stuff i dont fully get.

i want to learn the "rules" - stuff you are explaining but in more general terms so that if any colors are presented to me (either being added or shined somewhere, etc) then i can figure out the answer.

6. Sep 23, 2006

### dnt

like to start, whats the difference between adding and subtracting colors and how do you konw when either is being done?

7. Sep 23, 2006

### Chi Meson

OK, color is light. If you see red, then you are seeing red light.

White light is composed of "all colors" but for now let's just say "+red, +green, + blue = white."

If white light goes through a "red filter," the filter takes away the green and blue, therfore it's "subtractive." It filters out everything except red.
So instead of calling a red filter "red," call it "-green, -blue."

OK, are you with me?