Are there standard colours for Australian road signs?

Yes. Information is referenced in AS 1743:2018: Road Signs – Specifications.

Non-reflective colours

Non-reflective road signs must closely resemble the colours outlined in AS 2700 - Colour Standards for General Purpose:

• 

  Red
  Colour R13 Signal Red

• 

  Yellow
  Colour Y15 Sunflower

• 

  Brown
  Colour X65 Dark Brown

• 

  Blue
  Colour B23 Bright Blue

• 

  Standard Green
  Colour G12 Holly Green

• 

  Green
  Colour G13 Emerald

Retroreflective colours

Retroreflective colours must closely resemble the space outlined in AS/NZS 1906.1

Fluorescent colours

Fluorescent colours must conform to common colour designations red, orange or yellow.