Extra_data_template: error - Formatting quoted scalar

Configuration
1

HI
I am trying to change

light.drawer:
  extra_data_template:
    if (attributes.rgb_color) return "RGB:" + attributes.rgb_color ; return null;

into:

light.drawer:
  extra_data_template:
    if (attributes.rgb_color) return "RGB: " + attributes.rgb_color ; return null;

because i need the extra space after the : , since now it show like this, which isn’t pretty:

01

i guess i can’t help the lack of spaces in the actual rgb’s but something like RGB:_218,93,65 would already be better, if i can’t reach this: RGB:_218,_93,_65

unfortunately i get this error,
while scanning a quoted scalar\n in \"/config/customize/customize_light.yaml\", line 134, column 44\nfound unexpected end of stream\n

which i am not yet familiar with, and wouldn’t know how to solve, hence my post to you all.

Hope you could have a look and point me to an answer?
Strange thing is "_RGB" is valid … "RGB_" isnt.

Cheers,
Marius