Colours of text and Command: Help

Can you explain me the meaning of white colour inside a sequence?
Most of command are in light blue, but sometimes the colour is white.

For example, in my Frost mage Macro:

/cast [combat] Freeze (Freeze is light blue)
in the next line (they are both in Post Macro)…
/cast [combat] Waterbolt (Watelbolt is in white, like [combat])

/cast [nochanneling] Ebonbolt (Ebonbolt is in white)
this last in located in the Main Sequence.

All other commands are in light blue.

Thank you in advance