The orange colour of dichromate solution changes of blue on heating with alkalies due to the formation of chromate ions.

Explanation

**Step-by-Step Solution:**

1. **Identify the Compounds:**
- The dichromate ion is represented as \( \text{Cr}_2\text{O}_7^{2-} \), which is known to have an orange color in solution.
- The chromate ion is represented as \( \text{CrO}_4^{2-} \).

2. **Understand the Reaction:**
- When dichromate ions are heated with alkalis (basic conditions), they undergo a transformation to form chromate ions.
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