Best way to have Blinkt! display a solid color?

You can import set_clear_on_exit and use set_clear_on_exit(False) to prevent Blinkt! being cleared when your code exits.

But ideally you need to run a script continuously to display a solid colour, this is because the APA102 LEDs on Blinkt! can very easy interpret environmental noise as signal and display something random.

To do that, you would write something like this:

import time
from blinkt import set_pixel, set_brightness, show, clear

set_brightness(0.1)
clear()

FPS = 15

# set all pixels to RED
while True:
    for i in range(8):
        set_pixel(i, 255, 0, 0)

    show()
    time.sleep(1.0 / FPS)