A colour change is when the current candle is:

• ascending and the previous one was descending;
• descending and the previous one was ascending.

Here is the code:

MySma   = average[20,0](close)
Rising  = MySma > MySma[1] AND MySma[1] < MySma[2]
Falling = MySma < MySma[1] AND MySma[1] > MySma[2]

Just a way to do it (many other options to color based on conditions)

MySma   = average[20,0](close)
Rising  = MySma > MySma[1] AND MySma[1] < MySma[2]
Falling = MySma < MySma[1] AND MySma[1] > MySma[2]

if rising then 
 r = 0
 g = 255
elsif falling then 
 r = 255
 g = 0
endif 

return mysma coloured(r,g,0)

You can use the indicator’s properties (settings) to add colour zones.

This is the code that mimicks the properties, but is not as good:

MySma   = average[20,0](close)
Rising  = MySma > MySma[1] AND MySma[1] < MySma[2]
Falling = MySma < MySma[1] AND MySma[1] > MySma[2]
if rising then
   r = 0
   g = 255
elsif falling then
   r = 255
   g = 0
endif
IF close > MySma THEN
   OO = close
   HH = close
   LL = MySma
   CC = MySma
   DrawCandle(OO,HH,LL,CC) coloured(0,128,0,16)
ELSIF close < MySma THEN
   OO = MySma
   HH = MySma
   LL = close
   CC = close
   DrawCandle(OO,HH,LL,CC) coloured(255,0,0,16)
ENDIF
return mysma coloured(r,g,0)