Repro steps:
1) Open the project and demo scene.scene
2) Change the Graphics API for iOS to GLES2/3
3) Build and run it on newer device, that supports Metal (f.e. iPhone6+)
4) Notice that the depth texture produces blue artifacts(screenshot 1)
5) Change the API to Metal or build and run it on an older device (f.e. iPad2)
6) Notice there are no more blue artifacts (screenshot 2)

Actual/Expected behaviour can be seen in screenshots

Reproduced in: 5.3.4p4; 5.2.4f1
On 5.4.0b16 depth texture is not working at all on Metal devices
Reproduces only on GLES2 and GLES3, no artifacts when API is metal