Specifiyng color of polygons drawn by mahotas.polygons

Question

I am using this code

with open('frame 0001.json') as json_file:
    json_dict = json.load(json_file)
    shape = (1920, 1052)
    canvas = np.zeros(shape)
    for obj in json_dict["objects"]:
        pts = [((round(p["x"] - 1)), (round(p["y"]))) for p in obj["polygon"]]
        mp.fill_polygon(pts, canvas, obj["classIndex"])
    pic = canvas.transpose()
plt.imshow(pic)
plt.show()

to convert an JSON file into a plot. However, I would like to change the colors which are first set by obj["classIndex"] to another color. While printing the plot, I found out that the plot looks like this

[[5. 5. 5. 5.]
 [5. 5. 5. 5.]
 [5. 5. 5. 5.]
 ...
 [4. 4. 4. 4.]
 [4. 4. 4. 4.]
 [0. 0. 0. 0.]]

I have never seen this before. how would I go about to change these values into RGBs? That I set before. I know I could use

colors = [
    (0, 0, 0, 255),
    (100, 100, 100, 255),
    (204, 0, 0, 255),
    (0, 174, 0, 255),
    (102, 51, 153, 255),
    (0, 0, 155, 255),
    (255, 102, 0, 255),

for idx, c in enumerate(colors):
    pic[np.all(pic == idx)] = c

to change something like this

[[0 0 0 0]
 [0 0 0 0]
 [0 0 0 0]]

to this

[[0 0 0 255]
 [0 0 0 255]
 [0 0 0 255]
 [0 0 0 255]]

however, I have never worked with something like this before

[[5. 5. 5. 5.]
 [5. 5. 5. 5.]
 [5. 5. 5. 5.]]