I think Bernie deliberately shrouds his economic message in color-blind wrapping paper. Whether that is out of philosophical belief or political expediency, it's hard to say. However, when you take that message to minority communities, they might not be convinced that you really understand their concerns if you can't speak to them as if you do. The Sanders campaign seemed to get caught up in the typical patronizing "I marched!" thing and the war of silly words from which we're supposed to divine that Hillary is actually a secret racist/homophobe.
I suspect, though I have no way of knowing, that when you are selling to minority communities, especially black communities, an economic message of a higher minimum wage and free college, the response is probably along the lines of, "Well, college and employment are heavily biased against us, so thanks for helping white people!" Bernie fans will point out, and they're not wrong, that Hillary isn't selling an economic message that spells out how she'll ensure that her economic policies correct for racial inequality, either. At least, not explicitly, not in speeches and not in debates. But due to longstanding trust among black voters, they feel comfortable that she'll look out for their interests.
Candidates always get caught up trying to be better on things like immigration and criminal justice reform and even gun violence than the other guy/gal because those issues matter to minority communities. Which they no doubt do, and probably much more personally than for most white people. But they aren't the only issues, nor are they necessarily the only important issues, that minority communities care about. After all, it's not the slightest bit out there, unfortunately, for black voters to hear a message about economic prosperity, and worry they'll be left behind. Because, well, they always are. I don't think Bernie Sanders ever gave any reason to believe he'd take specific action to ensure his reforms helped everyone. I think it was a deliberate choice by him, and I think it probably prevented him from really reaching deep into minority communities, and reaching black voters in particular.
After all, we like to pretend otherwise, but racial politics are still very tricky for Democrats. Poorer, rural and small-town white labor Democrats in Bernie's wheelhouse aren't particularly receptive to a non-color-blind economic message in a lot of cases. I don't think those demographics are all that different in that regard from Republicans. I think Bernie probably figured he'd do better running up margins among the young and the rust belt set, than if he made a pitch more targeted at minority audiences. He may have been right about that. The end result being, that young minorities liked Bernie just like young white people, while he had yuge difficulty breaking through with older minority voters.