OLPC Human Interface Guidelines/The Sugar Interface/Colors
Imbuing Color with Meaning
Sugar treats color differently than the typical UI: colors are used in the interface represent the individuals who are interacting within the mesh, not the activities or objects they are using. Children personalize their laptops and their presence on the mesh by selecting a dual-tone color scheme. All of the activities, objects, and comments belonging to a child take on her own colors—even when they appear on the laptops of other children on the mesh—forming a visual identity that supplements her name and attributes.
This color treatment extends even within activities. For instance, in the Web activity a link-sharing feature encourages children to browse the web in groups, sharing interesting or useful pages with each other. Each URL object posted for the others to view appears in the colors of the child who posted the link. Similarly, chat bubbles on the Bulletin Board take on the children's colors. Likewise, any object, text, or other interface element within your activities that corresponds to a particular child should be rendered in this manner. When the display runs in grayscale mode, this colored visual identity is less apparent. However, significant differences in value, according to the Munsell System, ensure that the XOs retain a level of visual distinction even in the absence of color.
To maintain a degree of purity to this system, interface elements, buttons, and other icons that belong solely to the activity and not to any particular child should remain in grayscale to the extent possible. While removing color as a primary visual clue may seem counter-intuitive, it does encourage the icon's form to clearly indicate its function. Since the laptops will also run in grayscale mode, clearly distinct shapes become essential in the absence of chroma information, and so limiting activity icons to grayscale by default ensures compatibility in both modes. Additionally, keep in mind that the traditional method of "graying-out" inactive buttons and controls simply will not function on the laptops and must be avoided. Instead, please adhere to the guidelines for inactive icons.
Contrast in the Munsell Colorspace
The basic color scheme for the laptop is constrained by the need to work in both color (backlight mode) and grayscale (reflective mode); thus we have chosen guidelines that ensure at least some achromatic contrast under all conditions. Further, sustained legibility of text is accomplished by a combination of colors whose achromatic contrast is large and whose chromatic energy is of low to moderate level. For this reason, we are striving for achromatic contrast of at least two Munsell value steps.
The default value for the Frame is N2.5; the default value for the background is N9. Therefore, to maintain sufficient contrast, the line values for icons that appear on both the Frame and the background should range between N5 and N7. The interior fill of those icons should maintain achromatic contrast with the line value, e.g., the fill color for an icon with a line value of N5 should be either ≤N3 or ≥N7.