Hello!
Recently my teacher gave me the job to make 2 tcs34725 with the same I2C adress. But I he forgets that I have only been in ICT class for 4 months now.. 
So I already made it so I 1 color sensor works with the arduino uno, but now I need to make it so there are 2sensors and connected with the STM32F103C8T6 Blue pill Arduino!
I dont know how to start or anything, havent seen any example code either, someone please help !
Thanks!
I am unfamiliar with this device, but it seems as if your teacher may be a bit of a sadist. 
A bit of googling brought up this page, which has several references to further documentation, including a 1200 page manual!
Good luck!
I would say that the first step will be to get the blink sketch uploaded and running on the blue pill. Next, get a single sensor running using the same sketch as on the Uno. Finally, introduce the second sensor.
I think OP is having problems using several I2C devices with the same I2C address, and no CS (chip select) pin.
This can be solved with an I2C multiplexer (Adafruit).
Leo..
Yes, an i2c multiplexer would work. So would using a software i2c library on the Uno to make a second i2c channel. The OP has already selected a solution, or has been told to use one. The "blue pill" is an Arduino compatible development board based on an STM32 chip and has two hardware i2c channels.
The main difficulty with the blue pill board, if I remember, is that they do not come with a bootloader installed. A serial programmer of some kind is required to upload the bootloader so that serial program upload can be used thereafter. Even then, I'm not sure the usb socket can be used for anything more than supplying power to the board.
I would prefer a Maple Mini clone over the blue pill. Although slightly more expensive, it comes with a bootloader installed and can be powered and programmed using its usb socket straight away. It has the same or very similar chip and also has two hardware i2c channels available.
If you are just starting with the Blue Pill, these 2 links may help. It is how I recently got started:
Official Guide:
http://wiki.stm32duino.com/index.php?title=Blue_Pill
A User's practical experience of setting it up.
Stm32f103 has two I2C interface, no i2c multiplier needed.
They are managed by ARM MBed framework, with "stmduino" I don't know.
Go to Stmduino website.