How to set tkinter scale slider's color?

To achieve what you want, we have to use a ttk style, so we need to use a ttk.Scale, however, it does not accept all the options of the tk.Scale you are using. Therefore, I suggest you to use the TickScale from the ttkwidgets module (See documentation here). This way you can combine the tk.Scale options with the ttk styling.

The idea is to:

1. create images of the desired color for the slider, e.g. withtk.PhotoImage:

   img_slider = tk.PhotoImage(width=30, height=15)img_slider.put("{<pixel_color> ... <pixel_color>} {<second line>} ...")

   I used a basic rectangle, but you can also load a more elaborated image if you wish.

2. create the colored slider theme element:

   style.element_create('custom.Horizontal.Scale.slider', 'image', img_slider,                     ('active', img_slider_active))

   I also used a different image img_slider_active, to highlight the slider when the cursor is on it.

3. Use the new element in a custom style

   style.layout('custom.Horizontal.TScale',             [('Horizontal.Scale.trough',               {'sticky': 'nswe',                'children': [('custom.Horizontal.Scale.slider',                              {'side': 'left', 'sticky': ''})]})])

4. Apply the custom style to your TickScale widget. Since the TickScale is based on a ttk.Scale, you need to use the style to set the background, foreground and troughcolor options, see full code below.

import tkinter as tkfrom tkinter import ttkfrom ttkwidgets import TickScaledef set_img_color(img, color):    """Change color of PhotoImage img."""    pixel_line = "{" + " ".join(color for i in range(img.width())) + "}"    pixels = " ".join(pixel_line for i in range(img.height()))    img.put(pixels)root = tk.Tk()# create images used for the themeslider_width = 30slider_height = 15# normal sliderimg_slider = tk.PhotoImage('img_slider', width=slider_width, height=slider_height, master=root)set_img_color(img_slider, "red")# active sliderimg_slider_active = tk.PhotoImage('img_slider_active', width=slider_width, height=slider_height, master=root)set_img_color(img_slider_active, '#1065BF')style = ttk.Style(root)style.theme_use('clam')# create scale elementstyle.element_create('custom.Horizontal.Scale.slider', 'image', img_slider,                     ('active', img_slider_active))# create custom layoutstyle.layout('custom.Horizontal.TScale',             [('Horizontal.Scale.trough',               {'sticky': 'nswe',                'children': [('custom.Horizontal.Scale.slider',                              {'side': 'left', 'sticky': ''})]})])style.configure('custom.Horizontal.TScale', background='black', foreground='grey',                troughcolor='#73B5FA')scale = TickScale(root, from_=0, to=100, tickinterval=100, orient="horizontal",                  style='custom.Horizontal.TScale')scale.pack(fill='x')root.mainloop()

slider.configure(foreground=color)

draws a rectangle around the slider, which distinguishes it from the trough. Setting the foreground color the same as the background color creates a difficult to find slider, as you stated.

Another option is to use a different theme (https://tkdocs.com/tutorial/styles.html). The snippet below allows you to see how your slider would look with different themes:

import tkinter as tkfrom tkinter import ttkclass App(tk.Tk):    def __init__(self):        super().__init__()        # root window        self.title('Theme Demo')        self.geometry('400x300')        self.style = ttk.Style(self)        # label        label = ttk.Label(self, text='Name:')        label.grid(column=0, row=0, padx=10, pady=10,  sticky='w')        # scale        slider = ttk.Scale(self, from_=1, to=10)        slider.grid(column=1, row=0, padx=10, pady=10,  sticky='w')        # button        btn = ttk.Button(self, text='Show')        btn.grid(column=2, row=0, padx=10, pady=10,  sticky='w')        # radio button        self.selected_theme = tk.StringVar()        theme_frame = ttk.LabelFrame(self, text='Themes')        theme_frame.grid(padx=10, pady=10, ipadx=20, ipady=20, sticky='w')        for theme_name in self.style.theme_names():            rb = ttk.Radiobutton(                theme_frame,                text=theme_name,                value=theme_name,                variable=self.selected_theme,                command=self.change_theme)            rb.pack(expand=True, fill='both')    def change_theme(self):        self.style.theme_use(self.selected_theme.get())if __name__ == "__main__":    app = App()    app.mainloop()