How are you powering the shield?
On my Arduino, I am using the +5vdc. (Works fine)
On the Teensy, I am using the power, from the USB (+5 VDC) Vin
Ut oh ... just realize the Teensy can power the shield at 5 VDC BUT the
Teensy 3.0 ARM is a 3 vdc device which means the I2C bus is running at 3.0 vdc logic ?
Probably need to obtain level converters OR Adafruit should design a RGB Display shield for 3 VDC and 5 VDC operation
Did you modify the "hello world" sketch at all?
Since Adafruit sells both the Teensy 3.0 and the Adafruit RGB I2C shield then it should be only a matter
of Adafruit hooking your RGB display to the Teensy 3.0 and tweaking the libraries, you designed, for proper operation.
Please note: I do not have any expensive professional test equipment to root-out this problem.
Yes, the two 4.7K resistors are pull-ups on SDA and SCL
The way the construction states both I2C pullups are on the top side of the RGB shield. By installing (soldering) the 2x16 display
there is no more access to these resistors.
The installation should require the user to install them on the back in case
there are modifications on the I2C bus.
What happens if you need to remove these resistors?
Also, you really should provide schematics for your kits.