Part of why you don't see colors in astronomical objects through a telescope is that your eye isn't sensitive to colors when what you are looking at is faint. Your eyes have two types of photoreceptors: rods and cones. Cones detect color, but rods are more sensitive. So, when seeing something faint, you mostly use your rods, and you don't get much color. Try looking at a color photograph in a dimly lit room.
As Geoff Gaherty points out, if the objects were much brighter, you would indeed see them in color.
However, they still wouldn't necessarily be the same colors you see in the images, because most images are indeed false color. What the false color means really depends on the data in question. What wavelengths an image represents depends on what filter was being used (if any) when the image was taken, and the sensitivity of the detector (eg CCD) being used. So, different images of the same object may look very different. For example, compare this image of the Lagoon Nebula (M8) to this one.
Few astronomers use filter sets designed to match the human eye. It is more common for filter sets to be selected based on scientific considerations. General purpose sets of filters in common use do not match the human eye: compare the transmission curves for the Johnson-Cousins UBVRI filters and the SDSS filters the the sensativity of human cone cells. So, a set of images of an object from a given astronomical telescope may have images at several wavelengths, but these will probably not be exactly those that correspond to red, green, and blue to the human eye. Still, the easiest way for humans to visualise this data is to map these images to the red, green, and blue channels in an image, basically pretending that they are.
In addition to simply mapping images through different filters to the RGB channels of an image, more complex approaches are sometimes used. See, for example, this paper (2004PASP..116..133L).
So, ultimately, what the colors you see in a false color image actually mean depends both of what data happened to be used to be make the image and the method of doing the mapping preferred by whoever constructed the image.
I think it's fair to say that the EHT image definitely is consistent with GR, and so GR continues to agree with experimental data so far. The leading paper in the 10th April 2019 issue of Astrophysical Journal letters says (first sentence of the 'Discussion' section):
A number of elements reinforce the robustness of our image and the conclusion that it is consistent with the shadow of a black hole as predicted by GR.
I'm unhappy about the notion that this 'confirms' GR: it would be more correct to say that GR has not been shown to be wrong by this observation: nothing can definitively confirm a theory, which can only be shown to agree with experimental data so far.
This depends of course on the definition of 'confirm': above I am taking it to mean 'shown to be correct' which I think is the everyday usage and the one implied in your question, and it's that meaning I object to. In particular it is clearly not the case that this shows 'Einstein was right': it shows that GR agrees with experiment (extremely well!) so far, and this and LIGO both show (or are showing) that GR agrees with experiment in regions where the gravitational field is strong.
(Note that, when used informally by scientists, 'confirm' very often means exactly 'shown to agree with experiment so far' and in that sense GR has been confirmed (again) by this observation. I'm assuming that this is not the meaning you meant however.)
At least one other answer to this question is excellent and very much worth reading in addition to this.
Best Answer
Yes, it's a false-color image. Radio telescopes don't detect visible light.
In the first of the six technical papers (which seem to be open access! they are listed in this summary article), the color scale is assigned a physical interpretation:
The interpretation is at the bottom: it's some kind of an effective temperature, with dark being "cold" and the brightest being six billion kelvin. There's a huge amount of detail in the technical papers.
I decline to speculate on why news organizations do or don't say things. But it sure is less confusing to look at false-color images that use modern perceptually-uniform color mappings.