The home processing of color photography in Czechoslovakia was possible since 50ties. For older Opemus enlargers (as Opemus 6x6, Opemus II, Opemus III) was produced special adapter, called Meocolor. Meocolor was inserted between bulb and condensor. At the top of adapter was inserted IR filter, color filters were inserted into the slot. Subtractive filters were from glass and coloured gelatine in sets with 12 pcs for cyan, magenta and yellow color. With this filters you could change every color with 5% increments. The filters was made by Agfa, ORWO and by Meopta (Subtracolor correction filters). The first color head produced by Meopta was Meochrom and was produced for Opemus 5 enlarger. Color III and Color IV was newer color heads for enlargers Opemus 6,7 and Magnifax 4. Glass - gelatine filters weren´t very well, because their colour wasn´t stable and they faded with years. It wasn´t recomended to buy older used filter for this reason.
The second method was additive color mixing, when you can use only three filter - yellow, red and green and you expose paper three times. This was very cheap, you could insert filter between lens and paper, but now is this method obsolete.