How to stop disappearing text in Tkinter ttk.Combobox under the clam theme: set readonly foreground

Why selected text disappears in a Tkinter ttk.Combobox with the clam theme, and how to fix it by mapping the readonly foreground color for readable styling.

When styling a ttk.Combobox in Tkinter with the clam theme, you might hit a puzzling UX glitch: the selected text looks like it disappears after interaction with the dropdown. The value is still there, but it becomes unreadable. The behavior doesn’t show up with themes like alt, so it feels theme-specific and inconsistent.

Reproducing the issue

The snippet below sets up a readonly Combobox under the clam theme, with white backgrounds. The selected option becomes invisible during interaction.

import tkinter as tk, tkinter.ttk as ttk

app = tk.Tk()

styler = ttk.Style(app)
styler.theme_use("clam")
styler.configure("TCombobox", fieldbackground="white", background="white")
styler.map("TCombobox", fieldbackground=[("readonly", "white")], background=[("readonly", "white")])

chooser = ttk.Combobox(app, state="readonly", values=("apples", "oranges", "bananas"))
chooser.set("apples")
chooser.pack(padx=40, pady=40)

app.mainloop()

What’s actually happening

Under the clam theme, the default color for foreground when the widget is in readonly and focus is white. If the fieldbackground is also white, the text becomes effectively invisible against the field. That’s why the value looks like it vanishes.

Fixing the styling

The resolution is to explicitly map the foreground color to something readable for the relevant state. Setting the foreground to black when the Combobox is readonly and focused restores visibility.

import tkinter as tk, tkinter.ttk as ttk

app = tk.Tk()

styler = ttk.Style(app)
styler.theme_use("clam")
styler.configure("TCombobox", fieldbackground="white", background="white")
styler.map(
    "TCombobox",
    fieldbackground=[("readonly", "white")],
    background=[("readonly", "white")],
    foreground=[("readonly", "focus", "black")]
)

chooser = ttk.Combobox(app, state="readonly", values=("apples", "oranges", "bananas"))
chooser.set("apples")
chooser.pack(padx=40, pady=40)

app.mainloop()

If you prefer, you can also set the foreground for readonly regardless of focus.

Why this detail matters

UI themes provide sensible defaults, but customizations can collide with those defaults in subtle ways. Here, a simple background change masked the text due to a theme-defined state mapping. Knowing how ttk.Style.map works and how states like readonly and focus interact prevents visual regressions and keeps the widget readable under different interaction states.

Takeaways

When you override fieldbackground or other visual properties on ttk widgets, also review the associated foreground mappings, especially for specific states used by your theme. A small, explicit state map for foreground ensures consistent readability and avoids surprises like “disappearing” selections in ttk.Combobox under clam.