I myself found the answer using python-docx docs,
Here is the correct code:
from docx import Document
from docx.shared import RGBColor
document = Document()
run = document.add_paragraph().add_run('some text')
font = run.font
font.color.rgb = RGBColor(0x42, 0x24, 0xE9)
p=document.add_paragraph('aaa')
document.save('demo1.docx')
"some text" is a parameter of the add_run () function, not the add_paragraph () function.
The above code gives the desired color.