When designing custom signage, it's important to consider how the color of your text will affect its readability from a distance.
If your design has a background, it's always best to use as much color-contrast as possible. This means a light background and dark text, or a dark background and light text, so that your message "pops" out from the background.
If your design has no background and is printed on a clear material (i.e. Clear Vinyl or Clear Static Cling), white (or very light-colored) text stands out the best on windows. Even if your window is not tinted, the eye will read the window as dark, so white or light text on top of it will be the most-noticeable. Any time a sign is being placed inside a window, use a test print from a home printer first to make sure your design or text can be seen. Even non-tinted windows can have UV coatings that restrict visibility from inside the window.
Always limit yourself to 2 or 3 different text colors when creating your design. Keep primary text in one color and supplementary text in another. Using too many colors looks cluttered, busy and confusing. If you are set on having a lot of colors, consider shades of the same color, which is less-distracting.