How do different tissue culture matrices affect background in fluorescent microscopy?
Extracellular matrix (ECM) fluoresces, especially Collagen and Laminin. The maximum is in the DAPI and FITC channels and the fluorescence becomes weaker towards longer wavelengths. However, since the coat on the TC flasks is very thin, I would not expect this to be a problem. The best thing is just to try it. There is also a quite famous document available which might be of help:

Autofluorescence: Causes and Cures