Swedish coin of wrong colour

I have two of these: https://en.numista.com/catalogue/pieces1502.html
One looks like in the picture on that page, but the other one is kind of yellow, like this: http://www.ebay.com/itm/ws/eBayISAPI.dll?ViewItem&item=140848495595&item=140848495595&lgeo=1&vectorid=229466

I have seen plenty of these coins as I grew up with them, but never before have I seen one that is yellow. What is this difference in colour? Are they different types or something? Does any of you know?

The one which is yellow is from 1970.

I think it's just the reflection of the light.

If I hold them next to each other I can clearly see there is a difference. It's like the difference between copper and nickel, or silver and gold.

This can be patina. Sometimes copper-nickel may even have a brown color. Everything depends of the conditions in which the coin was stored. I have a U.S. quarter in brown.

Does this mean I should throw it away, or should I be happy with my "gold"-50 öre coin?
Since it is so uniform, covering the entire coin, could it have been caused deliberately?

I got it in a bag together with two kg of coins from an antique shop.

A good picture of both coin will be nice !!  
you don't thing so  ?