Ignition expressions cannot do assignments. They are just expressions. An assignment to the bound property is implied (Imagine that property and an equal sign to the left of your first character in your expression).
I would use intermediate custom properties in place of the variables you’re using. Make boolean custom properties northHandOnly and southHandOnly on the indicator. Give them the conditions you have in the if blocks at the top.
Then for the color, bind it using the last if statement you have, but using the custom properties in the condition.
Assuming that 17SS_STRIPPER-HAND-S-END_I6-12 is a boolean, I don’t see the point in checking whether it is true or false, when in each scenario you are setting another bit to true and then ultimately if either of the resulting bits are true you are ending up a with the same color. You could strip your code down to a much simpler expression:
if({[default]200FT Stripper/SS_PB/13SS_N-END-HAND_I5-13},
color (71,255,71),
color (255,10,10)
)