What happens to the copper sulphate crystals when they are heated that causes them to change color?

Heating the CuSO4. 5H2O crystals causes then to loose the water of crystallisation that is the 5H2O part. It becomes anhydrous copper sulphate. Its colour changes to white from blue.

explanation:

venn diagram is pictorial representation with of circles showing the relation between two finite sets or things. the intersection part of two circles conveys the relation present in between those sets or things.

here in the venn diagram of sand and salt two circles represent sand and salt. but the area falling under the intersection of these circle represents the mixture of sand and salt.

so, in a venn diagram the mixture will be placed in a middle that is in between the intersection of two circles.