In the Online Designer you can edit all elements pixel perfect. Use the following tools for this:
What should be edited?
Click the element you want to edit: either the background, or an element uploaded image, clipart, text
Which tools can be used?
Pick either pen, color replacer or flood fill
Options for the tool
Choose color you want to paint with (in the sample it is dark green) and tool size (in the sample it is 5). You can switcht tools while editing and change the tool size.
Edit background or the element.
When choosing tool size 1, you can edit single pixel (=single stitches).
When using the color replacer, you can pick the color you want to paint with, and the color that should be replaced.
Click the green check to confirm and end edit mode.
This will set a redo point. Use this if you do larger edits, to do intermediate steps you can return to with undo function.
Color replacer is the most underrate tool. Use it to delete unwanted colors, and replace with desired colors.
With large tools size, you can replace a lot of astray / wrong pixel in no time, without having to click each one separatly.