I have not heard about colour problems.
Traditional Czech glass furnace had 6 melting pots - 5 colours + crystal. Cooling proces of free-hand shaped pieces was very long, days rather than hours. I try to get more information about this issue from old glassmakers, for the moment I did consider only design not technology.
Technology of free hand hot shaped glass was very popular in Czechoslovakia. I have found that many Czechoslovakian factories had produced this type of glass for some period, so the list of potential fabricators is relatively huge. In case I have no exact picture of pattern it is difficult to guess factory. Also Mstisov range was much bigger than I did ever expect, not only Harmony, Rhapsody, Pizzicato and Romana but also Opera, Rainbow, Riviera, Andrea and probably much more. It is really very exciting to investigate the mostly forgotten heritage of Czechoslovakian glassmasters.
Jindrich