This is a classic chemistry problem! It sounds like you're describing a solution containing an indicator. Here's why:

* Indicators are substances that change color depending on the acidity (pH) of the solution.

* Orange is a common color change for indicators in basic (alkaline) solutions.

Here are a few possibilities for the colorless solution turning orange:

* Phenolphthalein: A common indicator that is colorless in acidic solutions and turns pink/magenta in basic solutions. It might appear orange at a very high pH.

* Methyl orange: This indicator is red in acidic solutions, yellow in neutral solutions, and orange in basic solutions.

To determine the exact indicator, you would need more information, such as:

* The pH range of the solution before and after the color change.

* Other chemicals present in the solution.

Let me know if you have more details about the solution!