Hi Karen! On your iPad, iPod or iPhone go to your 'settings' button. This is not located within the sketchclub app -- it is the gray icon button that came preloaded on your apple device -- it is neutral gray and has little gears. Click on this button then scroll down towards the bottom of the page it takes you to until you find the button for 'sketchclub'. Click on this button and there are 6 or so adjustments which can be made to the sketch club app. Look for 'enable color picker'. If you want to completely eliminate the problem, turn it to 'off'. You need to reset it on each device. Here are the directions in summary
Settings > sketchclub > enable color picker (on/off)
You could also choose to leave it on but change the sensitivity with the slider located just below it.
The purpose of the color picker is to allow you to choose a specific color you have already used.
I expect the fact that this is happening on all of your devices means it is set too sensitive for how you regularly touch your canvas.
This is also what SpringTot was talking about, so maybe you already figured it out.