If you want to perform a transpo effect without using any playing cards or coin, then you are in the right place.
Write a color, let’s say WHITE, on the back of your business card. Ask the spectator to sign it and hold it. Then show your phone wallpaper, there’s a picture of a YELLOW rose.
With one simple touch, visually, the color of the rose turns WHITE, and the color on the spectator’s hand turns to YELLOW.
Guaranteed your spectator will be amazed. This is great for walk around or street magic.
It’s Modern. Easy to do. Examinable, spectator can keep your business card as a souvenir.

*This effect will only work if you have an Android phone*