How do I change the colour of an image in Pygame without changing its transparency?

In this version, the visible and transparent parts are the other way round to the original question as per Ankur’s suggestion.
Here is the essential working code:

import pygame, sys
from pygame.locals import *
pygame.init()

def load_image(name):
    image = pygame.image.load(name).convert()
    return image

def resize(obj, w, h):
    global scale
    return pygame.transform.scale(obj, (int(w * scale), int(h * scale)))


pink = (255, 0, 160)
red = (255, 0, 0)
peach = (255, 118, 95)
blue = (0, 0, 255)
blue_1 = (38, 0, 160)
dark_yellow = (255, 174, 0)
green = (38, 137, 0)
orange = (255, 81, 0)
colour = [pink, red, peach, blue, blue_1, dark_yellow, green, orange, green]
clock = pygame.time.Clock()
scale = 4
screen = pygame.display.set_mode((292 * scale, 240 * scale),0, 32)
banner = load_image("banner.png") #292x35
zero = load_image("zero.png") #5x7
c = 0
while True:
    for event in pygame.event.get():
        if event.type == QUIT:
            pygame.quit()
            sys.exit()
    rgb = colour[c]
    c = c + 1
    if c > 7:
        c = 0
    pygame.draw.line(banner, rgb, (53, 21), (53, 27), 5) #line the same size as zero image
    banner.blit(zero, (51, 21)) #blit image with transparency over line
    large_banner = resize(banner, 292, 35)
    screen.blit(large_banner, (0, 0))
    clock.tick(120)
    pygame.display.flip()

pygame.quit()
sys.exit()

This code for drop all color brightness

    def drop(surface):
        w, h = surface.get_size()
        for x in range(w):
            for y in range(h):
                r = surface.get_at((x, y))[0]
                if r>150:
                   r-=50
                g = surface.get_at((x, y))[1]
                if g>150:
                   g-=50
                b = surface.get_at((x, y))[2]
                if b>150:
                   b-=50
                a = surface.get_at((x, y))[3]
                surface.set_at((x, y), pygame.Color(r, g, b, a)) 

    img = pygame.image.load("image.png").convert_alpha()
    drop(img)

I solved this problem a little bit differently than others appear to, but I was trying to figure this out and the answers listed here did not give me exactly what I was looking for. I’ve slowly built off of what I’ve found to to accomplish my goals.

Firstly, I just wanted to change the colour of my animation frames to a random colour chosen from a list. The method I discovered used pygame.PixelAray() and .replace() to swap one colour for another:

self.fire_frame_list = glob.glob("pictures\Boom_Pow\Colour_Flame\*.png")
self.fire_frame_list.sort()
self.fire_frame_anim = [pygame.PixelArray(pygame.image.load(path)) for path in self.fire_frame_list]
...
self.fire_img = self.fire_frame_anim[self.frame_index]
self.fire_img.replace(self.colour, self.new_colour)
...
self.colour = self.new_colour
self.new_colour = randRGB()

In this code I gather the paths of my animation frames, sort them, and then load and convert the images into PixelArays. I seclect my current image using a variable called frame_index, and then change the colour for that frame. However, when I decided to change the colour midway through the animation, I encountered a problem; the second half of my animation – the frames that came after I had changed the desired colour – were their original colour – white.

In order to remedy this, I had to ensure that all the animation frames had their colour changed upon creation.

self.fire_frame_list = glob.glob("pictures\Boom_Pow\Colour_Flame\*.png")
self.fire_frame_list.sort()
self.fire_frame_anim = [pygame.PixelArray(pygame.image.load(path)) for path in self.fire_frame_list]
for img in self.fire_frame_anim:
    img.replace((255,255,255), self.new_colour)

For a while this worked perfectly, until I tried using this code with a translucent image. I made sure to use .convert_alpha() on my image so as to keep my base colour as white and have the alpha value be the changed value. This worked, but not with my PixelArrays.

Although printing a list of my pixels with each RGBA value listed showed the correct values, .replace() only changed the colour of the pixels with full opacity, leaving the rest white. After much experimenting, I realized I needed to create a list of my pizel alpha values using the same method I had used to check that .convert_alpha() had given me the values I wanted.

self.img = pygame.image.load("pictures\Boom_Pow\Bubbloid.png").convert_alpha()
self.pix = {self.img.get_at((i, j))[3] for j in range(10) for i in range(10)}
self.img = pygame.PixelArray(self.img)

for a in self.pix:
    self.img.replace((255, 255, 255, a), self.colour + (a,))

To start, I loaded my image and converted it to its alpha values. Next, I created a dictionary where each key was a possible pixel alpha value – the [3] is the index number for the alpha values in the colour list. Using dictionary keys ensured that I would not have any duplicate items. I then converted my images into PixelArrays and ran a loop that changed the colour for each of my possible alpha values.

This has been working the way that I wish, however I believe it is important to state that I only had 4 levels of transparency, and I do not know how python would handle having to run through tens or even hundreds of levels of transparency. However, this method works for the simple images I have created, and I hope I was able to help someone else as well.
Many of my little bubbles, filled with a random colour
My lantern, colour change midway through animation