a het for lue mosiac glider would look like
It would look like a mosaic glider.
The leucistic trait is recessive and the het is short for heterozygos or 'one gene' indicating that the glider MAY OR MAY NOT carry one copy of the Leu gene. If it is 100% het - because one of its parents was a leu gliders and would have contributed the leu gene - you cannot see it in the glider's color. If it has a lower percentage the only way to know if the glider actually carrys the leu gene would be to breed the glider to another leu or leu het glider and have them produce a leucistic joey. Then you know both parents carry the gene.
If the glider appears to be a standard grey - it may still carry the Leu gene as described above - but it would NOT have the dominant gene for the mosaic coloration. If the glider has a mosaic gene - it will have mosaic traits such as white hands and feet and patches of white where you would normally find grey or black markings.