The colours of road signs have very specific meanings:
White and black signs are regulation signs. This means if you disregard what is on the sign, you’re breaking the law.
A sign with a Yellow background is a warning, caution, or recommended speed sign.
Freeway & Highway Signs
Green signs are for distances and direction (exits)
Blue signs are for things you will find when you take the exit: food, hotel, gas, attractions, services, camping, boat launch, rest area, etc.
White and Black
White and Black signs are regulation signs; you must follow what is on the sign (it is not optional). In this case it looks like you can drive up to 110 km/hr but no more. Keep in mind it’s always up to the driver to decide an appropriate speed based on conditions (weather, road, driver experience, condition of vehicle/tires, etc.)
Orange signs are construction and/or temporary signs. Here we have a “Crew working” sign and an “Obstruction – keep left” Sign.
Obstruction, keep left. These signs are very helpful in the dark.
Yellow signs are warnings usually about upcoming hazards. Here the road will curve to the right up ahead. If you’re looking far ahead in this case you can see the curve in the road. Since there is no speed advisory, you should be able to go the speed limit here without any issues (providing for conditions, of course).
Traffic may be merging soon. Check your rear-view and/or right mirror and try to time things to help the merging traffic onto the freeway.
Pedestrian Crosswalk Signs
Yellow signs are warning or caution signs while white & black signs are regulation signs.
See also: School and Playground Signs