The colored line stops when I reach the black line of the drawing!
ColorStudio HD has a feature called "Stay Inside The Lines", designed to help less experienced artists color within the lines. As the name implies, that feature ensures that any continuous line will stop when it reaches the black border of any foreground elements (the parts of the picture that move when animation is turned on).
To turn this feature off, tap the gear icon on the right side of the coloring page to open the Settings Menu. Tap the word "On" beside "Stay Inside the Lines" to turn it off.