Part of the allure of stucco is its natural look. The feel of the mortar and the earthen qualities of the stucco mean you likely do not want brazen oranges for your exterior stucco surfaces. As a result, most stucco colors center on earth colors, neutral colors or pastels. For red brick, which is a rich but not bright color, there are plenty of options, and if you need to modify it later, you can repaint stucco in most colors available for exterior paints.
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An off-white or ivory color keeps the stucco on the light side. Not as likely to have the intense glare of a pure white in the sun, the ivory tone has less of an edge. Ivory and similar off-whites will match red brick, and no special fine tuning or other considerations are required. It's a no-fail match.
Gray, like ivory and the off-whites, has little or no color (or hue, to be precise) component, so there's no chance of conflict with the red brick. A lighter gray will match the typical mortar color. It can be a bit drab, though, especially if the stucco wall covers a large area. If you wish to select gray, consider a minute addition of a warm red or rust color to sympathize with the red of the brick and add a little color.
Earth colors will fit nicely with the earthen red of the brick, while bringing more hue to the structure than gray or ivory. You can take three approaches with earth tones. Brownish tones, such as smoky taupe or milk chocolate, provide a solid match without any dynamic color relationship to the red brick. Warmer tones, such as russet, with a hint of orange, are a bit more colorful and link with the red brick's warmth. Green earths, such as sage, provide a complementary contrast that is bolder, without being too blaring.
Pastel colors are a way to impart more color to the stucco. The drawback is you lose a bit of the natural, stone-like effect. You may be prepared to make this sacrifice, bringing more color to the surface, but there's more chance of conflict. Keep the pastel on the light side. The darker the pastel, the greater the chance for conflict with the red brick, especially with colors close to red, such as orange or magenta. Safer pastels are soft mint, light pink or pale ocher.