The Significance of the Various Colors of Highway, Road, and Street Signs

Question: What is the difference between green highway signs and blue highway signs?

Answer: There are several colors of signs that are used on the city streets, county roads, state highways, and interstate highways throughout the US (Canada and Europe will be somewhat different, but will still have their own color codes per country).

So, rather than give you a simple answer, as usual, I'll give you a complex answer to a simple question. Actually, I'll give you a color coded answer with visuals so you'll have a good understanding of how highway, road, and street signs work.
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The most common highway and road signs are white with black or red copy (mostly), with the exception of stop and yield makers. Such are known as regulatory signs and include:

Stop
Yield
Speed limit/zone (Including "Reduced Speed Ahead" type signs)
Directional arrow ("One Way" signs fit into this sub-category)
Lane control (such as "Left Turn Only" signs or "Bus Lane" signs)
Passing ("Do Not Pass," "Pass With Care" etc.)
Prohibitive ("Do Not Enter" and "No Trucks" are examples of this type of sign)
Parking (e.g. "Handicapped Parking" or "No Parking 12am to 6am")
Restrictive (e.g. "Weight Limit 20,000 Lbs")
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While this list is certainly not exhaustive, it should give you a pretty good idea of regulatory signs as you've seen them all you life, obey them every day (hopefully), but just weren't aware of the significance of white.

The next major category is the yellow signs. Such are generally permanent warning signs that are placed in areas where there is always a reason to warn you of something, like a sharp corner. Some examples of these signs are:
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Stop Ahead
Winding Road (symbol only usually)
Signal Ahead
Narrow Bridge
Lane Ends
Bump
Slippery When Wet
Slow Children
Truck Crossing
Et Cetera - there are over 200 signs in this category

In the same category, with some crossover signs which can be yellow or orange, are the temporary warning signs. These are used for a temporary traffic situation and include over 100 signs as well, although between the yellow and orange category, the total is just over 300 signs. These include:

Detour
Be Prepared to Stop
Two Way Traffic
Gravel
Water Over Road
Bump
Lane Closed Ahead
Road Work Ahead
Flagger Ahead
Road Closed
Et Cetera
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A relatively small but important category is the School Zone signs. These are now, in many area, a super reflective fluorescent yellow-green color, and signify that there are children present in the area at many times of day. These areas are often heavily patrolled by the police, so, if you don't want a speeding ticket, these are signs you'll really want to pay attention to. They include:

School Zone symbol
What Hours Zone Signs are in effect
End School Zone
Et Cetera

And (drum roll) finally, we're getting to your question about blue versus green signs. I'll start with green signs first. In the US, almost universally, green signs have to do with where you're at and where you're going. These include:

School Zone symbol
What Hours Zone Signs are in effect
End School Zone
Et Cetera

The blue signs are also directional signs, but have to do more with things like hospitals or parks or fuel or lodging. These signs include:

"H" signs - for hospital
Tent symbol for camp area
Gas Pump symbol for Fueling Station
Rest Area signs
Knife/Fork/Plate symbol for Restaurant
Et Cetera

Lastly, the brown signs. These are similar to the blue signs, but are generally pointing to recreational areas or motorist services within recreational area. The symbols are similar to the blue signage ones with some overlap. The symbols you'll see on these include:

Bear Symbol for a bear viewing area (kind of a scary sign, really!)
Helicopter symbol for heli-pad
Dog symbol for pet rest area
Hiker symbol for hiking trail
Bed symbol for lodging
Downhill Skier symbol for an upcoming ski area
Cross Country Skier symbol for XC skiing trails
Sailboat symbol for sailing access area
Et Cetera

So, there's your highway sign primer. It covers most of the signs used on roads, streets, highways, and interstate highways in the US, so hopefully you got not only your original question answered, but several others too!

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