Since these often did not have a Columbus tube decal as a "rule of thumb' the blue paint points to a 2nd tier frame tubing, either Aelle or Zeta, if it was red paint it would be SL or perhaps SLX depending on year or make. Here's a quote attributed to an employee of Ochsner (Chicago importer) from another thread:

"...It is correct that there were only two colors. Red and Blue. The red used the more expensive Columbus SL or SPX tubing and were made by Royal of Switzerland, with a very small number being made by Seratta [SP] on the East Coast USA.

The blue frames were also manufactured by Royal in Switzerland. The blue ones came in two types of Columbus tubing, the higher end Aelle and the Zeta."