(In reply to some thoughts
by K Sengupta)
First line: "begin at the end of the spectrum."
We know that:
"Newton divided the spectrum into seven named colors: red, orange, yellow, green, blue, indigo, and violet (this order being popularly memorized by schoolchildren using the mnemonic ROY G. BIV)."
Conclusion: Red is indeed at the end of the visible spectrum.
It may also be noted that:
"Purple is a general term for the range of shades of color occurring between red and blue.........In color theory, a 'purple' is defined as any non-spectral color between violet and red. The spectral color violet is not a purple."
Conclusion: Purple can be regarded as a shade of red
Second line: "then add the numeral ten"
It is widely known that "X" is the roman numeral for ten.
Third line: "next find our personal pronoun"
We know that the objective personal pronoun for "we" is "us".
Thus, in conformity with first through fourth lines, we now have: "purple" + "X" + "us" = PurpleXus, which is phoenitically similar to "perplexus".
Consequently, the required answer to the riddle is "perplexus".