I would recommend you just get males if you don't want many females, as it's quite important to have more females than males. What will happen, you ask - the females will simply get harassed to death and die of stress. The ratio should be 2 females per male, or just all males.
In your case this would either be 6 males, or 4 females and 2 males. So if you want a colorful tank just get all boy guppies.