Other way around CT, blue pump with blue regulator is for higher pressure applications (hence higher price because it can pump greater volumes of fuel supposedly), red pump and regulator for low pressure applications.
I recently bought a blue pump and regulator (with a spring out of a red regulator installed) for the lower pressure application - dellortos which you are right do prefer lower pressure (~3-6psi).
Holley externally-mounted electric fuel pumps are also available in various flow ratings. The "red" pump, P/N 12-801, is rated at 97 GPH and it is designed to work with stock or mildly modified engines. Pressure is pre-set to 7 PSI and a regulator is not required. The "blue" pump, P/N 12-802, is rated at 110 GPH and it is designed for street/strip applications. Pressure is pre-set at 14 PSI and a regulator is included as part of the package. Neither pump is compatible with methanol or alcohol fuels nor should they be used with fuel injection systems. The "black" pump, P/N 12-815, is rated at 140 GPH and is designed to work with either gas or alcohol fuels. This one is similar to the "blue" pump but it kicks out more fuel. These pumps all feature a simple, yet rugged, rotor and vane design which has proved itself over the years.
This info is from :
http://www.holley.com/HiOctn/TechServ/TechInfo/FMFPTech.html
[Edited on 12-2-2003 by Dasdubber]