I wanna create a program that.....

Question

.... has box with original color black but takes color from user and slowly changes its color to the one given by the user
any help

Answer 1

Then learn a language of your choice, depending what the type of application it is.
If it's a desktop app use something like C# / C++ or Java
For a phone, those languages works as well but C++ / Swift is preffered.
For a website, php / js and html and css would do the trick :)

In the end it's mostly up to what you prefer.