Explanation:

The basic purpose of this doctrine is to determine under which head of power or field i.e. under which list (given in the Seventh Schedule) a given piece of legislation falls.

Pith means ‘true nature’ or ‘essence of something’ and Substance means ‘the most important or essential part of something’.

Doctrine of Pith and Substance says that where the question arises of determining whether a particular law relates to a particular subject (mentioned in one List or another), the court looks to the substance of the matter. Thus, if the substance falls within Union List, then the incidental encroachment by the law on the State List does not make it invalid
Statement 2
The literal meaning of Colorable Legislation is that under the ‘color’ or ‘guise’ of power conferred for one particular purpose, the legislature cannot seek to achieve some other purpose which it is otherwise not competent to legislate on.

This Doctrine also traces its origin to a Latin Maxim:

“Quando aliquid prohibetur ex directo, prohibetur et per obliquum”

This maxim implies that “when anything is prohibited directly, it is also prohibited indirectly”. In common parlance, it is meant to be understood as “Whatever legislature can’t do directly, it can’t do indirectly”.

In our Constitution, this doctrine is usually applied to Article 246 which has demarcated the Legislative Competence of the Parliament and the State Legislative Assemblies by outlining the different subjects under List I for the Union, List II for the States and List III for both, as mentioned in the Seventh Schedule.

This doctrine comes into play when a Legislature does not possess the power to make law upon a particular subject but nonetheless indirectly makes one. By applying this principle the fate of the Impugned Legislation is decided