In both of these poems, Langston Hughes expresses his concerns about how Whites are not truly seeking to understand Blacks, and how White culture is appropriating and using the products of the Harlem Renaissance for their own gain.

In "Visitors to the Black Belt," Hughes explains how people outside of Harlem - mostly Whites - look in for brief moments and think they understand how life there is, when really they have no idea.  They have a false sense of understanding - a superficial view that they somehow think captures the essence of what Harlem truly is, when it really just scratches the surface.

Hughes points out that Whites "can talk about/across the railroad tracks ... up in Harlem," and they "can say/Jazz on the South Side," and with these descriptions, they somehow think they are "in the know" about life in Harlem.  They drive in on the weekends, listen to jazz and blues in the clubs, watch the entertainers, drink at the bars, then return to their homes to live out the rest of their week.

By contrast, to Hughes, Harlem is "here/on this side of the tracks."  It's the only home he knows.  Whereas to Whites, the South Side means "jazz," to Hughes,  
    

...it's hell 
On the South Side:

Kitchenettes
With no heat 
And Garbage
In the halls.

He knows the poverty, the hopelessness, the sense of loss that often accompanies life in Harlem.  He rather defiantly asks at the end, "Who're you, outsider?" He then requests, "Ask me who am I."  He advises the Whites not to think they know him, his home, his problems and concerns, his way of life, until they actually spend some time with him and get to know him.  Harlem is more complex than what they see on the surface.

In "Notes on Commercial Theater," Hughes speaks with an angrier tone as he complains that Whites have somehow stolen bits of Black culture - the products of the Harlem Renaissance - and tried to make them their own.  He accuses:

You’ve taken my blues and gone -
You sing ‘em on Broadway
and you sing 'em in Hollywood Bowl,
And you mixed 'em up with symphonies
and you fixed ‘em
So they don’t sound like me.
Yes, you done taken my blues and gone.
You also took my spiritual and gone.

Whites have appropriated the sounds of the Black community and tried to remake them as their own.  Not only have they used these sounds in their own shows, such as Macbeth, Carmen Jones, and The Mikado, but what's worse, they have left the Blacks themselves OUT in many ways, for they don't include the music in "what's about me," Hughes argues. 

Hughes predicts, though, that this injustice cannot last forever.  He says:

But someday somebody’ll
Stand up and talk about me,
And write about me - 
Black and beautiful -
and sing about me,
And put on plays about me!

Eventually, he believes he will see himself on stage and in movies - the White community cannot try to hide and ignore him forever.  They will finally recognize his true beauty and regret having failed to see it for so long.