Just curious if anyone knows why the graphics, colours, formats, shapes of road, street, and highway signs in Singapore & Hong Kong share tons of similarities.

Take a look at these:

Arrow-shaped direction sign in Singapore:
http://www.streetdirectory.com/stock_images/travel/simg_show/11158973820487/1/east_coast_parkway_expressway_ecp_exit_10b_/
Photo courtesy of Robert Stenier

Arrow-shaped direction sign in Hong Kong:
http://image46.webshots.com/47/3/29/39/2081329390055681816mziVDo_ph.jpg
Photo courtesy of ramonyu

As one can see from both photos, the arrow-shaped sign indicating to the left have green backgrounds, white edge coloured frames, white lettering, white arrow. So can anyone provide insights to why the two places can share so many similar characteristics in this area?

Don't forget both HK and Singapore were the British Colonies! They just do what the British did! ;)

Correct a lot of things in singapore all come from Britain, same as Hong Kong, some example can be as big as education and can be as small as signboards and all tht...

The background and text colours are designed to make it easier for drivers to see them, so the range of colours is actually quite limited around the world.

Most of the these road building follow the british "road note 29" with all the details and specifications.