The spot where the colors overlap is a result of painting two separate brush strokes in Multiply mode, one red, the other blue – in other words, the brush was set to Multiply and it was painted on a Normal layer. The place where they overlap is a result of the second stroke influencing the appearance of the first. The result would be the same if, with the brush blend mode set to normal, you were to paint each stroke on a separate layer and set each layer’s blend mode to Multiply.
In this instance, the first stroke (red) is called the “Base” color. The second stroke (blue) is called the “Blend” color. The color that happened where they overlapped is called the “Result” color. You will have to remember these terms in order for the rest of this to make sense.
Normal Mode: This is the default blend mode for layers and brushes. At 100% opacity, any base color is ignored. The blend color and result color should be the same. The result color will change at the same rate that you reduce the opacity of your brush or layer. Anyone who’s mixed watercolors or similar paints will understand this pretty easily. Keep in mind that when painting at less than 100% opacity the result color will be different from the blend color, even if the blend color and the base color are the same.
Dissolve Mode: Similar to normal mode, except the result is an even distribution of “spattered” pixels based on the brush in use. Let me skip an overly complicated explanation of Dissolve by saying that it will give you lots of dots if you use a soft-edged paintbrush or airbrush. Lowering the opacity on the brush gives more spread to the spray rather than changing the result color.
Behind Mode and Clear Mode: These are not layer blending modes, but modes for certain brushes. They really have nothing to do with blending, so I will limit my explanation of them to say that Behind mode paints on transparent pixels ONLY, while Clear mode changes painted pixels to transparent pixels.
Multiply Mode: You may have heard of this one before. Out of all the more-complex blending modes, this one is the easiest to understand because there is a simple real-world analogy. Multiply mode is like coloring in a coloring book with magic markers – you can’t alter black lines and over-lapping colors produce a different darker color. The reason it’s called “multiply” is because this mode takes the number value of the base color and multiplies it by the blend color to arrive at the result color, which is always darker. Multiply won’t change black because you can’t get any darker than black, and it isn’t influenced by white because there’s no color information to multiply with. The darker the base color or blend, the closer to black the result color will be.
