Python: Hero-o-matic 2

# guizero - Hero name generator
from guizero import App, Text, ButtonGroup, Combo, PushButton, TextBox, Picture, Slider

app = App(title="My Version of Hero-o-matic", width=720, height=640, bg="#ffcccc")

# Function definitions for your events go here.

def validateColour(colour):
    validColours = ["pink","magenta","red","orange","yellow","green","cyan","blue","violet","brown","grey","black","white"]
    colourdefs=[(255,204,204),(255,0,255),(255,0,0),(255,153,51),(255,255,0),(51,255,51),(0,255,255),(0,0,255),(153,0,204),(102,51,51),(153,153,153),(0,0,0),(255,255,255)]
    for counter in range(len(validColours)):
        if validColours[counter]==colour.lower():
            txt_output.text_color=colourdefs[counter]

def makeIt():
    heroName = tbx_nam.value+", the "+btg_adj.value+" "+tbx_col.value+" "+cmb_ani.value
    txt_output.value = heroName
    txt_output.show()
    validateColour(tbx_col.value)

def darklite():
    darkness = int(sld_darkness.value)*3*17
    app.bg=(255,darkness,darkness)
    picnames=["ebook-penguin.png","judo-penguin.png","VR_penguin.png","Christmas-in-July-penguin.png","veggie-penguin.png","painter-penguin.png"]
    img_header.image=picnames[int(sld_darkness.value)]

# Your GUI widgets go here
txt_title = Text(app,"Hero Name Generator", size=36)
img_header = Picture(app,"veggie-penguin.png")
sld_darkness = Slider(app,start=0,end=5,horizontal=True)
sld_darkness.value=4


txt_nam = Text(app, text="Type your name:")
tbx_nam = TextBox(app, width = 15)

txt_adj = Text(app, text="Choose an adjective:")
btg_adj = ButtonGroup(app, options=["Artful", "Brazen", "Confusing", "Droll", "Engaging"], selected="Amazing")

txt_col = Text(app, text="Enter a colour:")
tbx_col = TextBox(app, width = 15)

txt_ani = Text(app, text="Pick an animal")
cmb_ani = Combo(app, options=["Ankylosaurus", "Brachiosaurus", "Ceratosaurus", "Dimetrodon", "Einiosaurus"], selected="Aardvark", width=20)

btn_makeName = PushButton(app, text='Make my hero name now',command=makeIt)
txt_output = Text(app, text="Hero name will appear here", size=28)
txt_output.hide()

# Set up event triggers here
sld_darkness.when_mouse_dragged = darklite

# Show the GUI on the screen, start listening to events.
app.display()