First touch with python decorator
When using decorators, you should familiarize yourself with functools.wraps. Consider the difference in available informations between these two (useless) decorators:

from functools import wraps


def decorate1(func):
    def wrapper(*args, **kwargs):
        return func(*args, **kwargs)
    return wrapper


def decorate2(func):
    @wraps(func)
    def wrapper(*args, **kwargs):
        return func(*args, **kwargs)
    return wrapper


When applied to a function:

@decorate1
def test1(x, y, z):
    "test1 docstring"
    print(x, y, z)


@decorate2
def test2(x, y, z):
    "test2 docstring"
    print(x, y, z)


The help on each function look quite different:

&gt;&gt;&gt; help(test1)
Help on function wrapper in module __main__:

wrapper(*args, **kwargs)

&gt;&gt;&gt; help(test2)
Help on function test2 in module __main__:

test2(x, y, z)
    test2 docstring




Since you’re using Python 3, you should consider using better timing primitives. Namely time.perf_counter():

def wrapper(*args, **kwargs):
    begin = time.perf_counter()
    res = original_function(*args, **kwargs)
    elapsed = time.perf_counter() - begin




Lastly, you should consider using format all along instead of string concatenation:

import time
import colorama
from functools import wraps


def timeit_decorator(original_function):
    @wraps(original_function)
    def wrapper(*args, **kwargs):
        begin = time.perf_counter()
        result = original_function(*args, **kwargs)
        elapsed = time.perf_counter() - begin
        print("Function {color}{}{reset} executed in {color}"
              "~{:.2f}{reset} minutes!"
              .format(
                  original_function.__name__,
                  elapsed / 60,
                  color=colorama.Fore.GREEN,
                  reset=colorama.Style.RESET_ALL))
        return result
    return wrapper