Acid fast organisms are -

Spores may be seen in unstained preparations as Refractile bodies. The forespore stains intensely but once the spores envelope is laid down the spores does not stain readly. Spores appear as unstained areas in Gram-stained preparations but being more acid fast than the vegetative cells they can be stained by a modification of the Diehl -Nelson technique. Ref: Ananthanarayan & paniker's Textbook of Microbiology 9th edition pg no 21