Introduction:  Relationships are the key to successful gardens - the difference between a collection of plants and a harmonious composition. Color (along with texture) is the cornerstone of garden design.

The best insight I can provide is to have the courage to be daring with your garden.  Be a rose gardening risk-taker...

For every rule, there's an exception.
Color in the garden is affected by the seemingly infinite colors found in flowers (as described by hue, saturation, and tone), time of day, amount of shade, amount of cloud cover, and reflectance from adjacent plants.  This makes it very difficult to provide a hard-and-fast list of rules for matching colors, but...here are some suggestions:
 

Do...realize that every gardener has their success and failures.  Experiment, and don't hesitate to move plants that clash.
Do...create 'pockets' or 'groups' of plants which are harmonious in their relation to each other.  Separate these groups using green, white, and silver, or bridge these groups by using colors that provide for transition (for example, golden yellow and lemon yellow may clash, but consider transitioning by using an intermediate yellow - one which falls on the color scale between golden yellow and lemon yellow).

Do...use white to bridge clashing colors.  White unifies the garden.
Do...use silver to bridge clashing colors.
Do...remember that blue is not an impact color, but rather an enhancer of other colors.  Blue is a wonderful compliment to pink roses.
Do...combine blue and yellow, blue and pink, blue and red.
Do...remember that the classic 'old rose' color scheme is pink, blue, silver, and gray.  Use it!

Do...remember that red is a superb accent color in the perennial garden; red roses planted as singles can be stunning.  To continue the thought...
Do...plant soft colored roses in greater numbers for more visual impact.  For example, plant 3 or 5 or more (plant in odd numbers) soft pink or apricot roses.
Do...remember that yellow is the color best perceived by the human eye - thus be especially careful when mixing yellows.   Keep yellows separated, or work for a graceful transition - placing hot yellows next to cool lemon yellows can spell trouble.
Don't...be afraid to use orange (sparingly).  In the perennial world, orange is not often used by the 'refined gardener'.  However, there are some absolutely stunning orange roses around, so if you like a particular rose, be a rebel!  Plant orange roses in small percentages to the overall garden (even in a 'hot' garden), or they will visually dominate the landscape.
Don't...mix magenta and orange, or pink and orange.

Celebrate yourself, for the greatest gift a gardener can give is to make their own unique vision a reality.  Show me something I've never seen.

White Roses | Red Roses | Pink Roses | Yellow Roses | Orange Roses | Apricot Roses | Mauve Roses | Multicolored | Meaning of color