Different color pure sulfate mgo board

Mgo board can be a different color, like white, grey, green, etc.
When we produce the grey color mgo board, what we put is ferric oxide.
In china, lots of suppliers use fly ash to produce grey color mgo board.
The chemical characteristic for fly ash is very unstable, when the fly ash mix with the other mgo board raw material, the chemical reaction is very hard to control. So it is very easy to meet the problem after the customer got the grey color mgo board, they find the color is inconsistent, some part dark grey, some part light grey. So we do not suggest use fly ash to produce different color mgo board, we only use ferric oxide to produce different colors.