uses the Adafruit wheel function and a generator to iterate back and forth over a range of colors.

infinite_generator_neopixel.py

from adafruit_circuitplayground.express import cpx
import time

def wheel(pos):
    # Input a value 0 to 255 to get a color value.
    # The colours are a transition r - g - b - back to r.
    if pos < 0 or pos > 255:
        return (0, 0, 0)
    if pos < 85:
        return (255 - pos * 3, pos * 3, 0)
    if pos < 170:
        pos -= 85
        return (0, 255 - pos * 3, pos * 3)
    pos -= 170
    return (pos * 3, 0, 255 - pos * 3)

def cycle_colors(startpos=0, endpos=255, step=1):
    i = startpos
    step = -step
    while True:
        print(i)
        yield wheel(i)
        if startpos >= i or i >= endpos:
            step = -step
        i += step


color = cycle_colors(startpos=150, endpos=225,step=3) 
while True:
    for i in range(len(cpx.pixels)):
        cpx.pixels[i] = next(color)
        cpx.pixels.show()
        time.sleep(0.1)