Pandas assign - passing column in a user defined function

Question

Given an input dataframe and string:

df = pd.DataFrame({"A" : [10, 20, 30], "B" : [0, 1, 8]})
colour = "green" #or "red", "blue" etc.

I want to add a new column df["C"] conditional on the values in df["A"], df["B"] and colour so it looks like:

df = pd.DataFrame({"A" : [4, 2, 10], "B" : [1, 4, 3], "C" : [True, True, False]})

So far, I have a function that works for just the input values alone:

def check_passing(colour, A, B):
    if colour == "red":
        if B < 5:
            return True
        else:
            return False
    if colour == "blue":
        if B < 10:
            return True
        else:
            return False
    if colour == "green":
        if B < 5:
            if A < 5:
                return True
            else:
                return False
        else:
            return False

How would you go about using this function in df.assign() so that it calculates this for each row? Specifically, how do you pass each column to check_passing()?

df.assign() allows you to refer to the columns directly or in a lambda, but doesn't work within a function as you're passing in the entire column:

df = df.assign(C = check_passing(colour, df["A"], df["B"]))

Is there a way to avoid a long and incomprehensible lambda? Open to any other approaches or suggestions!