looking for simplified version of motion capture for simplified situation where objects are solid and have no joint (no internal degree of freedom)

The whole question is about a simplified algorithm for tracking a single solid object which has no joint, with assumption that i have full control on adding some markers in real world to it.

For example i want to find full coordinates (Center of orange Coordinate system and direction of each orange axis) of the car in the following image: Assume i have control over adding as many markers(Stars) with required features(Shape, color, position) to my object(dreamy car) in real world.

Notice i am looking for some algorithms which mainly rely on finding position of my markers, which could be detected very fast by some simple color threshold.

Fast way could be to convert your image to HSV format and then apply color thresholding as you have mentioned. Here is a short snippet which could get you started quickly.

import cv2 as cv2
import numpy as np

fn = 'image_or_videoframe'
# OpenCV reads image with BGR format
# Convert to HSV format
img_hsv = cv2.cvtColor(img, cv2.COLOR_BGR2HSV)

# Choose the values based on the color on the point/mark
lower_red = np.array([0, 50, 50])
upper_red = np.array([10, 255, 255])

in this case, the red is filtered in the image and masked_red would contain only the red pixels in the image.