Rainbow color combinations are often used with unfortunate effect on old houses, because the combinations are neither historically accurate nor appropriate for older neighborhoods.

But picking a combination that is "appropriate" is not easy. For owners of old homes, there are several basic guidelines, a few working rules and a number of sources of information that can make the job easier.

There are two basic guidelines. The first is to be a good neighbor. Remember that unless your house is in the middle of a farm, the colors you chose will affect not only your property but that of everyone around you.

It is especially important to remember this if you own a rowhouse or a semi-detached dwelling. The best solution is to work with your neighbors before you paint to see if you can agree on common colors or schemes.

Second, let the personality and character of the house dominate your selection. If you like the colors of the desert Southwest but are living in an 18th century house, keep your personality and color choices on the inside. Sand and terra cotta were not colonial colors. If you have a choice, take the historically accurate alternative. It will be the safest and most attractive.

There are two good published guides to painting the outside of an old house. They are also good introductions to the issues of historic house restoration and rehabilitation.

These books -- George Stephens' "Remodeling Old Houses Without Destroying Their Character" (Alfred A. Knopf, $3.95) and "Rehab Right" (City of Oakland, Calif., Planning Department, $6.95) -- are available at some local bookstores and through the bookshop of the National Trust for Historic Preservation. A review of the two suggests a few working rules for picking exterior colors.

Rule 1. Limit your selection to no more than three colors. "Rehab Right" suggests a light or muted color for the body of the house and a compatible darker shade for the base, trim and window moldings. Both sources agree on using white for the moving parts of the window.

Rule 2. Remember the roof. Since your house will be seen most often from the street, go outside and look at it. Notice the color of the roofing material and how the roof relates to the facade of the house. If it is a dominant part of the appearance, count its color as one of the three colors.

Rule 3. Beware of very bright colors and combinations of warm and cold colors (such as red and blue) or colors of the same intensity such as traffic light green and red.

Stephens' book suggests building a cardboard model of the front of the house. It does not have to be totally accurate but should have the right proportions of roof to facade and windows to facade. Paint the window areas black since that is how they will appear from the outside. Use the model to try out possible color combinations.

There are other ways of selecting color combinations. By taking paint samples from the house you can find out the original colors and duplicate those. The technique is explained in a technical leaflet called "Paint Color Research and Restoration," published by the American Association for State and Local History. A reprint is available for $1 by writing the association at 1400 Eighth Avenue South, Nashville, Tenn. 37203.

The association suggests using a surgical scalpel or model-maker's knife to expose each paint layer under a microscope or magnifying glass. The Munsell Color Co. of Baltimore will, for a fee, tell you its color code for the sample. Since the coding system is recognized throughout the paint industry, a paint store can use the code to duplicate both the color and finish of the paint. There are also historic paint consultants who will do the job for you.

Because house paint colors are so important to the character of a neighborhood, a number of local historical commissions and preservation groups across the country have developed paint color guidelines. The Cambridge, Mass., Historical Commission, for example, has published a "Guide to 19th Century House Colors." It lists appropriate exterior color combinations for various 19th century architectural styles.

The guide uses the Munsell system in identifying the colors and provides a brief description and illustration of the style. It is available for a fee by writing the commission at City Hall Annex, 57 Inman St., Cambridge, Mass.

A guide for owners of Victorian houses called "Exterior Decoration" was produced by the Athenaeum of Philadelphia. In addition to an essay on the use of color in Victorian architecture and an annotated bibliography, it has plates showing Victorian colors on houses on the period and paint chips keyed to the plates.