But it's a blatant error to mix up ‘seeing red’ with showing that you see red! I know what seeing red is & I know what showing … is. Couldn't we say that knowing what showing … is, is seeing

showing now what is knowing what seeing is. Consider the proposition: He makes sure what it means to him by … . Would you say the word had meaning to him if it ‘meant something else’ every time? And what is the criterion of the same colour coming twice.
In knowing what seeing red is you seem to give yourself a sample || you say to yourself ‘seeing red is this’ but you don't because the usual criteria for the sameness of the sample don't apply. I can say I call ‘red’ always the same colour or I whenever I explain red I point to a sample of the same colour.

(2015–) Wittgenstein Source Bergen Nachlass Edition (WS-BNE). Edited by the Wittgenstein Archives at the University of Bergen under the direction of Alois Pichler. In: Wittgenstein Source, curated by Alois Pichler (2009–) and Joseph Wang-Kathrein (2020–). (N) Bergen: WAB.