( ( ( ( ( ( If ( ( this light ) ( is ( in ( the ( visible region ) ) ) ) ) ) ( you ( ( can actually ) ( ( see ( a change ) ) ( in ( ( the color ) ( of ( the assay ) ) ) ) ) ) ) ) , ) and ) ( these ( are ( called ( colorimetric assays ) ) ) ) ) . )
(ROOT (S (S (SBAR (IN If) (S (NP (DT this) (NN light)) (VP (VBZ is) (PP (IN in) (NP (DT the) (JJ visible) (NN region)))))) (NP (PRP you)) (VP (MD can) (ADVP (RB actually)) (VP (VB see) (NP (DT a) (NN change)) (PP (IN in) (NP (NP (DT the) (NN color)) (PP (IN of) (NP (DT the) (NN assay)))))))) (, ,) (CC and) (S (NP (DT these)) (VP (VBP are) (VP (VBN called) (NP (JJ colorimetric) (NNS assays))))) (. .)))
If this light is in the visible region you can actually see a change in the color of the assay, and these are called colorimetric assays.
(ROOT (S (NP (PRP We)) (VP (VBP call) (NP (DT the) (JJ only) (NN light)) (SBAR (IN that) (S (NP (NNS people)) (VP (MD can) (VP (VB see) (NP (JJ visible) (NN light))))))) (. .)))