The DT 175 I added to my stable appears to be sapphire blue but according to the vin check silver and red were the only colors offered in 79.  It was built 10/78.  I am just wondering if this is normal.  VIN matches on motor and frame.  I love the color and excited to have my first DT in 41 years.

1980 DT 175 G had a Sapphire Blue option . Perhaps a previous owner has swapped out
the fuel and oil tanks .

2N5 would be the VIN prefix on a 79.  Several minor frame changes in 1980 to accommodate moving the oil tank to the right and the air box to the left compared to 79... but fuel tank and side covers didn't change mounts  (Air box and oil tank are completely different between 79 and 80.)

So yes, someone could have swapped the tank and side covers and/or repainted...  It sounds like the decal indicates it's a US model?   No additional Canadian sticker or anything?  (Other countries got different color options sometimes)

79 DT125 came in diamond blue...    side cover decals would have said 125 though... prefix 2N4. 
 

Following on from Mark's suggestion , which I hadn't considered .
I checked the brochure for the DT 125 F . Diamond Blue is a very dark shade of Blue ,
quite unlike the colour of the bike on your avatar . Unfortunately , no picture or colour
sample on the DT 175 G brochure , so still only a guess at this stage .

Serial number is 2N5.  I am sending pics also.

Here are some pics.  I had a Red 1980 Dt175 growing up and finally found a great bike.  I need 

Very nice bike.  That's one of the best and most fun models Yamaha ever made. 

The guy that sold it to me was so helpful. He had it listed on Facebook. He is probably on here too. He said the oil pump was rebuilt by the enduro doctor. Now I need to either find someone to install it or do it myself. I love playing with my motorcycles but I haven’t worked with a pump before.

I thought this picture was sent.