This is a special Bhogi rangoli idea - drawing 2 lines of different colours. Double line rule is the same for both types - , one colour ( usually white ) or 2 colours.
Pick the rangoli powder ( one colour each on the tip of the index finger and the next finger ) close with the thumb and push .
Simultaneously move the arm to draw the lines. One line falls between the index and next finger, the other line falls outside the index finger.
simple double line rangoli for beginners
This image ( close up ) shows how to draw two lines . Use of thumb is shown
Now for some simple 2 line muggulu
The information in this post may be useful if you are looking for
a)Double line rangoli images
b) Simple double line rangoli