Gray pavers, typically used for outdoor stone patios, come in a range of tones. The neutral gray can be lighter or darker, but usually it is near a middle tone. Because gray is so easy to match, you don't have to worry about making a mistake. Select the stucco color based on other color considerations.
The general idea with stucco is to provide a natural look. For that reason, you generally find off-whites, grays, light browns or similar neutral colors employed. However, stucco also comes in darker or more richly hued tones. Warm, peachy colors or adobe-type hues are available, as are darker colors like mahogany. Choose one to your taste, but be aware that the more color saturation in the stucco the less natural it will appear.
Conservative matches will stick to neutral colors. Ivory, flax and sand are good examples. A wide array of grays are available, too, but the gray-on-gray effect might be too bland for your home. Light russet is a good warm tone with a touch of color. For a cooler choice, try taupe, which has green umber undertones.
If you want a bolder effect, decide first if you prefer a warmer or cooler offset to the gray pavers. One way to decide is to review the yard and see if your outdoor furniture, foliage or surroundings suggest colors to match up with or contrast against. Cooler colors like eucalyptus or green clay are good medium tones; mint is a lighter choice. Warm tones like pale orange or mustard are viable options. You might even try a bluish shade, like pale ultramarine, for something unusual.