With v12.0 or v12.2 the color of the error bars match the PlotStyle
; however, with v12.1.1
$Version
(* "12.1.1 for Mac OS X x86 (64-bit) (June 19, 2020)" *)
ListPlot[{
{{1, Around[1, 0.1]}, {3, Around[2, 0.1]}},
{{2, Around[2, 0.1]}, {4, Around[1.5, 0.1]}}},
PlotStyle -> {Red, Darker@Green},
PlotLegends -> Automatic]

A workaround is to replace each RGBColor
with the associated PlotStyle
Legended[
Show[
ListPlot[
{{1, Around[1, 0.1]}, {3, Around[2, 0.1]}}, PlotStyle -> Red] /.
RGBColor[__] :> Red,
ListPlot[
{{2, Around[2, 0.1]}, {4, Around[1.5, 0.1]}},
PlotStyle -> Darker@Green] /. RGBColor[__] :> Darker@Green,
PlotRange -> All],
PointLegend[{Red, Darker@Green}, Automatic]]

Red
in v12.0 and v12.2 on my Mac; however, in v12.1.1 I need to useListPlot[{Around[1, 0.1]}, PlotStyle -> Red] /. RGBColor[__] :> Red
$\endgroup$IntervalMarkersStyle
$\endgroup$