I can confirm that in the case of the Logik L4THUB10, Red still equals power (marked R, J1). (Renaults are good training that you should assume nothing from wire colours, but I accept my first post could have been more concise.) The design has evidently evolved from that of the LP4HUB10:
In the L4THUB10 the USB lead from the root hub powers the Genesys Logic GL850G (U1) directly, drawing just about 69mA in my observations (when plugged into a Raspberry Pi), with no other downstream devices connected, [rising to 72mA with a bus powered USB 1 Hub added downstream of the powered Logik Hub, and rising to 85mA with the Logik Hub unpowered]. The voltage from either USB port of my Pi seems to be a lowly 4.3V (4.75V on GPIO), when the other port is supplying 3.3V to my Wifi. If I unplug the wifi, I can see about 4.5V on the USB (and 4.84V on GPIO), but voltage doesn't seem to be an issue for any devices I've tried so far. My Pi PSU (I've tried several sources) is generally 700mA or better.
For comparison, using a Compaq Mini: 68mA with no other downstream devices connected, [rising to 74mA with a bus powered USB 1 Hub added downstream of the powered Logik Hub, and rising to 90mA with the Logik Hub unpowered]. The Compaq Mini USB Root Hub voltage is 5.1V
On the L4THUB10, all 4 ports are powered from a common 5V rail, which draws power from the higher of the voltage of the external supply, or the root hub voltage minus the Schottky diode (D1) 0.4 V forward voltage drop. Potentially, a Hub power interruption can suck a lot of current from the Pi.
The Genesys Logic GL850G datasheet (apart from expressing Power Dissipation in units of mA) indicates that the current varies as a function of how many ports are active and whether they are Full Speed or High Speed. It should be noted that for almost all permutations and combinations, the current of the GL850G is stated as more than 100mA, and a maximum of 180mA. This appears to be the current to generate the comms, not the current to power any downstream devices.
An extract from the datasheet reads
"5.2.3 SELF/BUS Power Setting
GL850G can operate under bus power and conform to the power consumption limitation completely
(suspend current < 2.5 mA, normal operation current < 100 mA). By setting PSELF, GL850G can be
configured as a bus-power or a self-power hub."
Given how critical to Pi operation the difference between drawing 100mA or 180mA max, it begs a question: Does the GL850G only achieve a normal operating current of below 100mA when configured for Bus Powered, or is that a basic current draw before comms are added in?
The datasheet suggests automatic switching can be performed between bus powered and self powered modes, although how this affects behaviour (or current draw) is not clear to me. However, in the L4THUB10, the PSELF signal seems to be pulled to (an internally generated) 3.3V, suggesting the device itself is set to Self Powered, but the GL850G is evidently Bus Powered from the way it gets power from the root hub. It is only the downstream devices that are drawing from the Hub PSU.
Would there be any harm in rewiring the L4THUB10 so that the GL850G is powered solely from the Hub PSU rather than from the Pi? Would the GL850G need to reset when the Root hub wakes up, in order to conduct whatever protocol is used to establish the best comms? Having read that the Raspberry Pi has polyfuse protection, and that the unpowered L4THUB10 will sink current into any connected loads at the time (presumably no more than 100mA each, until permitted to draw more), the L4THUB10 appears to need using with care near a Raspberry Pi. I'm actually tempted to leave the
Red wire cut, and bypass the diode so that the GL850G can only take power from the Hub PSU, and so that the other ports on the L4THUB10 cannot suck power out of the Pi when the L4THUB10 is unpowered. Or reverse diode D1 so that the GL850G can power from the Hub PSU (if available) and add a diode in the root hub power wire, so that the GL850G can power off the Pi if it needs to, but the Pi cannot sink current from the Hub PSU? Can someone with more wisdom advise on that?
Although the L4THUB10 hub sports a label indicating the Input is 5V, 500mA, I see no reason why each port cannot draw that unless the GL850G is programmed to limit the collective units of power to each intelligent downstream device. I'm not familiar with how one can determine how many units each device is requesting or being granted.
Paying closer attention to what combinations work, or otherwise, I see that I can have the Hub connected and I can run my wireless keyboard and mouse through the hub OK (although barely tested). Or I can ditch the hub and have the wifi, but the wifi will not work through the hub or alongside it (on the other Pi USB port, either way round) , and eth0 gets disrupted also.
So, having covered the power details, I suspect the USB issues pointed out by drgeoff above will prove to be at the heart of this, but if the Pi USB ports are limited to 100mA each then the L4THUB10 is taking it towards the red zone as more downstream devices are plugged into it, particularly so for High Speed devices which can potentially push the L4THUB10 to draw 180mA from the host, even when it is powered.