Use the spelling specified in the STE dictionary (American English spelling). Use a different spelling only if other technical publication specifications, style guides, contracts, or other official directives apply.
Examples:
Non-STE: The door is made of carbon fibre reinforced plastic.
(“Fibre” is British English spelling.)
STE: The door is made of carbon fiber reinforced plastic.
(“Fiber” is American English spelling.)
Non-STE: Change the colour of the display.
(“Colour” is British English spelling.)
STE: Change the color of the display.
(“Color” is American English spelling.)