Lipid in tissue is detected by-

Special stains for fat: Frozen sections stained with Sudan IV or Oil Red-O give an orange-red color to the fat. Osmic acid gives a black color Oil Red O is a lysochrome diazo dye used for staining of neutral triglycerides and lipids on frozen sections and some lipoproteins on paraffin sections. It has the appearance of a red powder with maximum absorption at 518 nm