Hydraulic and Pneumatic Power Systems Characteristics of MIL-H-8446 (Skydrol 500 A & B) hydraulic fluid are a. blue color, phosphate ester base, fire resistant, butyl rubber seals. b. light purple color, phosphate ester base, fire resistant, butyl rubber seals. c. light green color, phosphate ester base, fire resistant, butyl rubber seals.