Indiana Code Title 6. Taxation § 6-6-2.5-31

Sec. 31.  (a) Special fuel exempted under section 30(a)(8) of this chapter shall have dye added to it at or before the time of withdrawal at a terminal or refinery rack.  At the option of the supplier, the dye added may be either:

(b) The department may require that special fuel exempted under section 30(a)(8) of this chapter shall have a marker added to the special fuel not later than the time of withdrawal at a terminal or refinery rack.  The marker must meet the specifications required by the department.