You can use the Rich Text in the Add Panel on the left side of the editor to make changes to only a portion of the text.
How to change a part of text color
Select a part you want to change the color.
Select the bold effect then click on the canvas.
You can now select the bold part. Change the color of your choice.
Undo the bold effect
You can also change the font size and font by taking the steps above.
For more information on how to use the Rich Text Box, click here.
※ It is not possible to change only a part of the text in the normal text box.