What version are you using, painting in sculpt mode is very very new.
General Q&A note
Help us all to help you.
Please give full screenshots with any questions. With the relevant panels open.
Also, include the lecture time and name/number that is relevant to the problem/issue.
The screenshot can be done by Blender itself, via the ‘Window’ menu bar top left hand side.
On that menu drop down is ‘save screenshot’.
Close ups additionally where they help.
Unsure what you mean, but Blender offers besides a SCULPT mode, also a VERTEX-PAINT mode, or a TEXTURE-PAINT mode. For the last one, you need probably need uv-maps