What do you want, a policy confession from the editor of the Express?! No paper would be stupid enough to afford dissenters 'proof' of something like racism, so readers can do nothing but speculate and base that speculation on the factors that have already been put to you, ie political tenor, the paper's readership, cumulative examples of similar articles etc etc.
I don't think racism is the primary motivation for the current Sterling witch hunt in the Star, the Sun and the Fail either (the profits generated by clickbait are), but similarly if you're telling me that those 'Johnny Foreigner hating' publications' hatchet jobs on Sterling aren't motivated by racism or an intention to reinforce a racial stereotype to some or other degree, then I think that's as naive an opinion as the one held by those who see racism as the papers' primary motivational factor. Of course you could always end the debate by producing some categorical evidence that racism isn't at play here....... ;-)