Red wire in light fixture, no red wire in junction box
There is no standard for wire colors... Al least not for wire function.  Color is decided by the necessity of manufacturing cable. Often we get lucky and the colors in the cable line up with preferred colors for function.  

However you can get colored tape and code wires yourself by function.  The first rule of marking wires is always mark both ends of the same wire at the same time. 

Your setup needs 3 wires besides ground: 


Safety Ground (always green, green/yellow or bare) 
Neutral (always white or gray, though white isn't always neutral)
Always-hot (preferred: black, any color other than white gray green is legal)
Switched-hot (preferred: red, ditto)


I am fastidious about using colored wire or marking wires with colored tape, because it makes everything very clear.  My recommendation is to identify the wire that is appropriate, and mark it with red tape.  

That said, it may not be possible if the topology of the wiring in your walls does not match the requirement.  Home Depot frequently puts things on the aisle endcap (those are for impulse buys, you know) and people get them home and discover they just won't work with their existing wiring.

Here's what you do

The two blacks and whites come in two cables such as Romex cable.  Cable 1 is the supply cable, and contains supply hot and neutral.  It may or may not come via a switch.   

Cable 2 is one of three things: a switch loop with the two wires shorted by a switch (probably not); always-hot onward power to receptacles and other loads like a garage door opener; or switched-hot onward power to the other lamp.  We're rooting for that last one.   

Start by taking a survey of every load in the house.  Does every half of every receptacle have power?  Does every hardwired thing work, all lights, fans, garage door opener etc.? Sump pump?  If anything does not, take note of that.  This is for a baseline for comparison.  

Now, shut off the breaker and split and cap those four wires. Uncap a white/black pair from the same cable and hook them up to the light - black to black, white to white.  Cap off lamp red, it will be hot!  Does the light power up?  No? Then that is not the supply cable.  Try the other one.  

Now the motion sensor light is working because it is connected to the supply cable. 

The other cable is either always-hot onward to other appliances, or switched-hot to the other lamp.  Keep it capped off.  Do the survey again.  What has lost power now?  If you find any new things have lost power, you now know that black wire is always-hot onward to other loads. Leave it black.  

If nothing else has lost power, except the other lamp, then good chance this is onward switched-hot to the other lamp.  Get some red electrical tape and tag the black wire red.   

Now you join color to color, with the red-marked black wire going ot red, of course.  Expect 3 neutrals (white).