It is possible to place up to six different dyes on one oligonucleotide, but that can only be done with a very specific sequence of dyes and is of no practical use. We routinely place two dyes on an oligonucleotide, and can place up to four with some degree of flexibility in dye choice using a combination of synthesis reagents and an orthogonal linker scheme. However, any combination above two gets more problematic to synthesize and purify, which will affect purity and yield.  Please contact us to discuss your specific needs.